Refresh the official Deno sidecar pin to v2.9.1 after checking the upstream release notes.
Update Windows and Linux archive checksums in engine-sources.lock.json and replace the bundled macOS arm64 executable with the official v2.9.1 artifact.
- update npm dependencies, including Vite 8.1.0 and TypeScript 6.0.3
- update bundled Deno engine locks and macOS arm64 binary to 2.8.3
- add npm run check:updates for npm and engine freshness checks
- ignore local agent/planning notes and remove tracked internal docs