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/app/control/mod.rs

@@ -1631,7 +1631,6 @@ mod actions;
 pub(crate) mod vision;
 pub(crate) use actions::property_json;
 mod entities;
-pub(crate) use entities::erase_block_definition;
 #[cfg(not(target_arch = "wasm32"))]
 pub(crate) mod http_bridge;
 mod interactive;