- build.rs: BUILD_TIMESTAMP from build time via `date -u`
- GET /health: now returns build_timestamp
- GET /health/detailed: returns build_timestamp + resources block
(cpu_used/cpu_idle/memory/gpu usage)
- Add build.rs to generate BUILD_VERSION at compile time
- Update CLI to show full version: '0.1.0 (build: 2026-03-31 11:21:37)'
- Update health endpoints to return build version
- Add chrono as build dependency