feat(text): native OS spell-checker for text_audit (Windows/macOS/Linux)

Add cross-platform SystemSpeller abstraction with three backends:
- Windows: direct COM vtable calls to ISpellChecker (Win32 Spell API),
  no external crate — uses the same hand-rolled FFI pattern as
  file_association.rs. Handles ALL-CAPS words by also testing lowercase.
- macOS: NSSpellChecker via objc2/objc2-app-kit (already in deps).
- Linux: Hunspell .dic file reader + hunspell CLI pipe fallback.

text_audit gains three new parameters:
  system_spellcheck: true  — activate OS spell-checker
  language: en-US        — BCP-47 language tag (default: OS default)
  suggest: true            — include spelling suggestions

The agent dictionary and system speller work as a layered pipeline:
words matching the agent dictionary are accepted immediately; only
remaining words are forwarded to the OS checker.

Response includes a system_speller object (enabled, available, backend,
language) and an unrecognized_words array with handle, position, and
optional suggestions.

Integration test: text_audit_system_spellcheck_flags_misspelled_words
(20/20 p1_tests pass). Release build verified.

src/mcp.rs

@@ -1225,7 +1225,7 @@ fn tool_definitions() -> Value {
         {
             "name":"ocs_read",
             "description":"Discover capabilities and record schemas, or read state, complete database records, command manifests, entities, properties, kernel measurements and spatial relationships, history, events or operation status from a live OCS session.",
-            "inputSchema":{"type":"object","properties":{"ocs_session_id":{"type":"string","minLength":1,"description":"Value of session_id returned by ocs_sessions."},"op":{"type":"string","enum":READ_OPS,"default":"state"},"parameters":{"type":"object","description":"Operation-specific filters.","properties":{"name":{"type":"string","description":"Command name or record name."},"search":{"type":"string","description":"Case-insensitive command or record-type search."},"find":{"type":"string","description":"Text query string for text_search."},"match_case":{"type":"boolean","default":false,"description":"Case-sensitive text search."},"whole_word":{"type":"boolean","default":false,"description":"Match only whole words."},"ignore_accents":{"type":"boolean","description":"Ignore accents/diacritics in text (defaults to true when match_case is false)."},"scope":{"type":"string","enum":["all","active_space","blocks"],"default":"all","description":"Text search scope."},"check_terms":{"type":"array","items":{"type":"string"},"description":"List of terms or suspect misspellings to flag in text_audit."},"dictionary":{"type":"array","items":{"type":"string"},"description":"Known valid words for text_audit dictionary check."},"pairs":{"type":"array","description":"Find/replace pairs for dry-run simulation in text_audit.","items":{"type":"object","properties":{"find":{"type":"string"},"replace":{"type":"string"}},"required":["find","replace"]}},"dry_run_pairs":{"type":"array","description":"Alias for pairs in text_audit.","items":{"type":"object","properties":{"find":{"type":"string"},"replace":{"type":"string"}},"required":["find","replace"]}},"document_id":{"type":"integer","minimum":0},"path":{"type":"string","description":"Optional intended output path for audit; extension determines target format."},"target_format":{"type":"string","enum":["dwg","dxf"],"description":"Intended output format for audit."},"target_version":{"type":"string","enum":["R14","2000","2004","2007","2010","2013","2018","AC1014","AC1015","AC1018","AC1021","AC1024","AC1027","AC1032"],"description":"Intended CAD output version for audit."},"collection":{"type":"string","description":"Record collection, all for records, or omit to discover collections and schema types."},"handle":{"type":"string"},"handles":{"type":"array","items":{"type":"string"},"description":"Exact entity or record handles."},"type":{"type":"string","description":"Entity or record type filter; for record_schema, returns its complete type graph and writable field paths."},"layer":{"type":"string","description":"Layer name filter for query."},"detail":{"type":"string","enum":["summary","geometry","full"],"default":"geometry","description":"Entity detail returned by query."},"fields":{"type":"array","items":{"type":"string"},"description":"Return only these entity fields plus handle."},"paths":{"type":"array","items":{"type":"string"},"description":"Project RFC 6901 JSON Pointer paths relative to record.properties."},"where":{"type":"array","description":"All property filters must match.","items":{"type":"object","properties":{"path":{"type":"string"},"op":{"type":"string","enum":["eq","ne","lt","lte","gt","gte","contains","starts_with","ends_with","in","exists","not_exists"],"default":"eq"},"value":{}},"required":["path"],"additionalProperties":false}},"near":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"Rank planar curves by exact kernel distance to this world XY point."},"point":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"World point whose object snap the snap op reports."},"from":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"Base point for perpendicular and tangent snaps (snap op)."},"contains_point":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"Return closed planar curves containing this world XY point."},"bounds":{"type":"array","items":{"type":"number"},"minItems":4,"maxItems":4,"description":"Filter entities whose world XY bounds overlap [min_x,min_y,max_x,max_y]."},"intersections":{"type":"array","items":{"type":"string"},"minItems":2,"maxItems":2,"description":"Return exact kernel intersections between two planar curve handles."},"after":{"type":"integer","minimum":0,"description":"Event cursor."},"request_id":{"type":"string","description":"Operation id to query."},"offset":{"type":"integer","minimum":0},"limit":{"type":"integer","minimum":1,"maximum":10000}},"additionalProperties":false}},"required":["ocs_session_id"],"additionalProperties":false},
+            "inputSchema":{"type":"object","properties":{"ocs_session_id":{"type":"string","minLength":1,"description":"Value of session_id returned by ocs_sessions."},"op":{"type":"string","enum":READ_OPS,"default":"state"},"parameters":{"type":"object","description":"Operation-specific filters.","properties":{"name":{"type":"string","description":"Command name or record name."},"search":{"type":"string","description":"Case-insensitive command or record-type search."},"find":{"type":"string","description":"Text query string for text_search."},"match_case":{"type":"boolean","default":false,"description":"Case-sensitive text search."},"whole_word":{"type":"boolean","default":false,"description":"Match only whole words."},"ignore_accents":{"type":"boolean","description":"Ignore accents/diacritics in text (defaults to true when match_case is false)."},"scope":{"type":"string","enum":["all","active_space","blocks"],"default":"all","description":"Text search scope."},"system_spellcheck":{"type":"boolean","default":false,"description":"Use native OS spell-checker (Windows, macOS, Linux)."},"language":{"type":"string","description":"Language tag for spell-checker (e.g. 'fr-FR', 'en-US', 'de-DE', 'es-ES')."},"suggest":{"type":"boolean","default":true,"description":"Include suggested corrections for misspelled words."},"check_terms":{"type":"array","items":{"type":"string"},"description":"List of terms or suspect misspellings to flag in text_audit."},"dictionary":{"type":"array","items":{"type":"string"},"description":"Known valid words for text_audit dictionary check."},"pairs":{"type":"array","description":"Find/replace pairs for dry-run simulation in text_audit.","items":{"type":"object","properties":{"find":{"type":"string"},"replace":{"type":"string"}},"required":["find","replace"]}},"dry_run_pairs":{"type":"array","description":"Alias for pairs in text_audit.","items":{"type":"object","properties":{"find":{"type":"string"},"replace":{"type":"string"}},"required":["find","replace"]}},"document_id":{"type":"integer","minimum":0},"path":{"type":"string","description":"Optional intended output path for audit; extension determines target format."},"target_format":{"type":"string","enum":["dwg","dxf"],"description":"Intended output format for audit."},"target_version":{"type":"string","enum":["R14","2000","2004","2007","2010","2013","2018","AC1014","AC1015","AC1018","AC1021","AC1024","AC1027","AC1032"],"description":"Intended CAD output version for audit."},"collection":{"type":"string","description":"Record collection, all for records, or omit to discover collections and schema types."},"handle":{"type":"string"},"handles":{"type":"array","items":{"type":"string"},"description":"Exact entity or record handles."},"type":{"type":"string","description":"Entity or record type filter; for record_schema, returns its complete type graph and writable field paths."},"layer":{"type":"string","description":"Layer name filter for query."},"detail":{"type":"string","enum":["summary","geometry","full"],"default":"geometry","description":"Entity detail returned by query."},"fields":{"type":"array","items":{"type":"string"},"description":"Return only these entity fields plus handle."},"paths":{"type":"array","items":{"type":"string"},"description":"Project RFC 6901 JSON Pointer paths relative to record.properties."},"where":{"type":"array","description":"All property filters must match.","items":{"type":"object","properties":{"path":{"type":"string"},"op":{"type":"string","enum":["eq","ne","lt","lte","gt","gte","contains","starts_with","ends_with","in","exists","not_exists"],"default":"eq"},"value":{}},"required":["path"],"additionalProperties":false}},"near":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"Rank planar curves by exact kernel distance to this world XY point."},"point":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"World point whose object snap the snap op reports."},"from":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"Base point for perpendicular and tangent snaps (snap op)."},"contains_point":{"type":"array","items":{"type":"number"},"minItems":2,"maxItems":3,"description":"Return closed planar curves containing this world XY point."},"bounds":{"type":"array","items":{"type":"number"},"minItems":4,"maxItems":4,"description":"Filter entities whose world XY bounds overlap [min_x,min_y,max_x,max_y]."},"intersections":{"type":"array","items":{"type":"string"},"minItems":2,"maxItems":2,"description":"Return exact kernel intersections between two planar curve handles."},"after":{"type":"integer","minimum":0,"description":"Event cursor."},"request_id":{"type":"string","description":"Operation id to query."},"offset":{"type":"integer","minimum":0},"limit":{"type":"integer","minimum":1,"maximum":10000}},"additionalProperties":false}},"required":["ocs_session_id"],"additionalProperties":false},
             "outputSchema":read_output_schema(),
             "annotations":{"title":"Read OCS state","readOnlyHint":true,"destructiveHint":false,"idempotentHint":true,"openWorldHint":false}
         },