refactor(mcp): extract MCP core into shared chatlab-mcp package

Move MCP Server logic (tool registration, resource registration, schema
conversion) from apps/cli/src/mcp.ts to packages/mcp-server so both CLI
and Desktop can share the same MCP implementation.

- New package: chatlab-mcp (packages/mcp-server) with McpDatabaseManager
  interface abstraction
- CLI mcp.ts slimmed to thin entry (~37 lines) calling startMcpServer()
- Desktop helper prototype at apps/desktop/helper/mcp.ts for dev-time
  MCP without GUI
- All 8 MCP tools and 3 resources unchanged

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/cli/package.json

@@ -74,6 +74,7 @@
     "@openchatlab/sync": "workspace:*",
     "@openchatlab/tools": "workspace:*",
     "@types/better-sqlite3": "^7.6.13",
+    "chatlab-mcp": "workspace:*",
     "tsup": "^8.5.0",
     "tsx": "^4.21.0"
   }