feat: add build info (commit SHA + deploy timestamp) to health endpoint and admin sidebar

- deploy.sh writes .build-info with commit SHA and timestamp after git pull
- /health endpoint now returns version, commit, and deployed_at fields
- Admin sidebar footer shows version and commit SHA
- Hetzner docs updated: runner --config flag, swap, and runner timeout

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/deployment/hetzner-server-setup.md

@@ -1056,7 +1056,7 @@ After=network.target
 Type=simple
 User=samir
 WorkingDirectory=/home/samir/gitea-runner
-ExecStart=/home/samir/gitea-runner/act_runner daemon
+ExecStart=/home/samir/gitea-runner/act_runner daemon --config /home/samir/gitea-runner/config.yaml
 Restart=always
 RestartSec=10