Introduce a `typecheck` job to GitHub Actions that sets up pnpm and Node.js (v22), installs dependencies, and runs `pnpm typecheck` on the workspace. Make the `build` job depend on `typecheck`. Also add a `typecheck` script (`tsc --noEmit`) to packages/websocket/package.json to enable package-level type checking. This ensures TypeScript errors are caught before the build runs.