feat(plugin): name-addressed XRecord CRUD on the HostApi (API v8)

Add create/read/update/delete/list for XRecord objects under
named-object-dictionary paths to the plugin HostApi, with five additive
PluginRequest/PluginResponse variants, dispatch through the shared
handler, in-process HostSession methods and both out-of-process proxies.

- dictionary paths walk from the NOD root; create seeds missing
  dictionaries (ensure_image_dictionary bootstrap) and refuses existing
  names; update refuses missing ones; refusals precede the undo step
- entry group codes validated (1..=369, never 5/105); payload content is
  the plugin's own
- each mutating call is one undo step: the pending history snapshot
  restores the objects map byte-exactly, auto-created dictionaries
  included (tested)
- typed entries survive DWG and DXF write/reload round-trips (tested);
  update drops verbatim raw bytes so saves emit the new content
- bump API_VERSION 7 -> 8 with the build.rs version_info in lockstep,
  mirroring the v7 addition; MIN_SUPPORTED stays 3

crates/ocs_plugin_api/src/ipc/protocol.rs

@@ -200,6 +200,32 @@ pub enum PluginRequest {
     RunCommand {
         request: crate::host::CommandRequest,
     },
+    /// V8 (additive): create an XRecord under a named-object-dictionary path.
+    CreateXRecord {
+        dictionary_path: Vec<String>,
+        name: String,
+        entries: Vec<crate::host::XRecordEntry>,
+    },
+    /// V8 (additive): read the entries of an existing XRecord.
+    ReadXRecord {
+        dictionary_path: Vec<String>,
+        name: String,
+    },
+    /// V8 (additive): replace the entries of an existing XRecord.
+    UpdateXRecord {
+        dictionary_path: Vec<String>,
+        name: String,
+        entries: Vec<crate::host::XRecordEntry>,
+    },
+    /// V8 (additive): delete an XRecord and its dictionary entry.
+    DeleteXRecord {
+        dictionary_path: Vec<String>,
+        name: String,
+    },
+    /// V8 (additive): list the XRecord names under a dictionary path.
+    ListXRecords {
+        dictionary_path: Vec<String>,
+    },
 }
 
 /// Responses the host sends back for `PluginRequest`.
@@ -236,6 +262,16 @@ pub enum PluginResponse {
     SolidResult(Result<Handle, String>),
     TableResult(Result<Handle, String>),
     CommandResult(Result<crate::host::CommandOutcome, String>),
+    /// V8 (additive): handle of a created XRecord.
+    XRecordCreateResult(Result<Handle, String>),
+    /// V8 (additive): entries of a read XRecord.
+    XRecordEntries(Result<Vec<crate::host::XRecordEntry>, String>),
+    /// V8 (additive): handle of an updated XRecord.
+    XRecordUpdateResult(Result<Handle, String>),
+    /// V8 (additive): the removed XRecord, with its prior content.
+    XRecordDeleteResult(Result<crate::host::XRecord, String>),
+    /// V8 (additive): XRecord names under a dictionary path.
+    XRecordNames(Result<Vec<String>, String>),
 }
 
 /// Messages sent from the host to the plugin runner.