Cut Garmin sync API volume; dashboard/health/records/UI improvements

Garmin Connect sync:
- Incremental syncs now re-fetch only a 1-day buffer (yesterday + today)
  instead of the full lookback window every run. Full lookback applies on
  the first sync only. Cuts steady-state API calls ~10x.
- Beat interval is now configurable via GARMIN_SYNC_INTERVAL_MINUTES and
  surfaced to the UI; the sync toggle is relabelled to the real cadence.

Frontend:
- Collapsible sidebar; clearer logged-in user + role display.
- Unified Body Battery colouring between dashboard and health (shared util).
- Sleep score trend chart on health page.
- Segments + medals on the dashboard's most-recent activity.
- Segments tab on the Records page.

Repo hygiene: add .gitignore, untrack committed __pycache__/*.pyc.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/core/config.py

@@ -22,6 +22,8 @@ class Settings(BaseSettings):
     pocketid_client_id: Optional[str] = Field(None, env="POCKETID_CLIENT_ID")
     pocketid_client_secret: Optional[str] = Field(None, env="POCKETID_CLIENT_SECRET")
     pocketid_allowed_group: Optional[str] = Field(None, env="POCKETID_ALLOWED_GROUP")
+    # Garmin Connect — how often the beat scheduler runs the automatic sync
+    garmin_sync_interval_minutes: int = Field(30, env="GARMIN_SYNC_INTERVAL_MINUTES")
     # Files
     file_store_path: str = Field("/data/files", env="FILE_STORE_PATH")
     # Environment