Add root validation check

[szweibel]

What changed

• add one credential-free root check for backend tests and frontend lint/build
• document the command in the development runbook

Why

The live service had valid backend and frontend checks but no single repository-level validation entrypoint. The wrapper uses the existing uv and Bun commands and leaves Docker/Compose as the deployment artifact.

Validation

• 527 backend tests passed
• frontend lint, TypeScript, and Vite build passed
• shell syntax and diff checks passed

No deployment or infrastructure state changed.

[szweibel]

Closing as superseded: this exact root validation change landed through PR #3, and PRs #4 and #5 subsequently extended the same source gate. Keeping this draft open would duplicate already-merged work.