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>

app/templates_config.py

@@ -94,3 +94,12 @@ templates.env.globals["DEFAULT_LANGUAGE"] = DEFAULT_LANGUAGE
 templates.env.globals["LANGUAGE_NAMES"] = LANGUAGE_NAMES
 templates.env.globals["LANGUAGE_FLAGS"] = LANGUAGE_FLAGS
 templates.env.globals["current_year"] = datetime.now().year
+
+# Add build info (version, commit, deployed_at) for sidebar footer
+from app.core.build_info import get_build_info
+from app.core.config import settings as _settings
+
+templates.env.globals["config"] = {
+    "version": _settings.version,
+    **get_build_info(),
+}