Add comprehensive build identification to agent

- Add git hash (short and full), branch, commit date
- Add build timestamp and dirty/clean state
- Add build profile (debug/release) and target triple
- New `version-info` command shows all build details
- `--version` now shows version-hash format (e.g., 0.1.0-4614df04)
- Startup logs now include version hash and build info

Example output:
  GuruConnect v0.1.0
  Git:     4614df04 (clean)
  Branch:  main
  Commit:  2025-12-30 06:30:28 -0700
  Built:   2025-12-30 15:25:20 UTC
  Profile: release
  Target:  x86_64-pc-windows-msvc

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

agent/Cargo.toml

@@ -99,6 +99,7 @@ windows-service = "0.7"
 [build-dependencies]
 prost-build = "0.13"
 winres = "0.1"
+chrono = "0.4"
 
 [[bin]]
 name = "guruconnect"