fix(blocks): one block definition service for delete, rename and purge on every path

new src/scene/block_service.rs (references, delete, rename, purge candidates, name validation, one error type and message). The command-line RENAME, palette Remove, plugin API, control/MCP block_delete and PURGE all use it. Layout, xref, dynamic-block, anonymous and open-in-editor records are protected; PURGE removes an anonymous block only when nothing references it. PROTOCOL CHANGE: control/MCP block_delete refuses a referenced block unless force=true (erases referencing INSERTs in one undo step). New REST route DELETE /api/v1/blocks/{name}?force=true. MCP tool digest re-pinned. Undo labels are Delete block X, Rename block X to Y and Purge.

src/mcp.rs

@@ -28,8 +28,10 @@ const MODERN_PROTOCOL_VERSION: &str = "2026-07-28";
 /// The `tool_schema_digest_is_pinned` test fails whenever the MCP tool surface
 /// changes, so schema drift (new params, renamed tools) is always a conscious,
 /// reviewed edit — and clients can detect a stale bridge by comparing digests.
+///
+/// `block_delete` gained its optional `force` parameter.
 #[cfg(test)]
-const TOOL_SCHEMA_DIGEST: &str = "e7bd01696f57143d7139aeb75d53389450b1102b603f2ba4ace8122cc692070e";
+const TOOL_SCHEMA_DIGEST: &str = "c16572f139198d90807ede156370879106672ed97566c16ab6ae001c996059e8";
 const MAX_REQUEST: usize = 1_048_576;
 const MAX_RESPONSE: u64 = 16 * 1024 * 1024;
 const CACHE_TTL_MS: u64 = 3_600_000;