feat: implement Fitbit OAuth, Garmin MFA, and optimize segment discovery

- Add Fitbit authentication flow (save credentials, OAuth callback handling)
- Implement Garmin MFA support with successful session/cookie handling
- Optimize segment discovery with new sampling and activity query services
- Refactor database session management in discovery API for better testability
- Enhance activity data parsing for charts and analysis
- Update tests to use testcontainers and proper dependency injection
- Clean up repository by ignoring and removing tracked transient files (.pyc, .db)

FitnessSync/backend/tests/integration/test_segment_optimization.py

@@ -0,0 +1,42 @@
+
+import pytest
+from unittest.mock import MagicMock
+from sqlalchemy import func
+from datetime import datetime, timezone
+from src.models.activity import Activity
+from src.models.segment import Segment
+
+@pytest.fixture
+def mock_db_session():
+    return MagicMock()
+
+def test_optimization_logic(mock_db_session):
+    # Setup test data object
+    activity = MagicMock(spec=Activity)
+    activity.id = 256
+    activity.last_segment_scan_timestamp = None
+    
+    # 1. Reset
+    # Logic in original script: manually reset timestamp.
+    # Here we test the optimization logic steps.
+    
+    # Scene 1: last_scan is None. Logic should PROCEED.
+    last_scan = activity.last_segment_scan_timestamp
+    assert last_scan is None
+    # If the logic in Job Manager checks `if last_scan >= max_seg_date`, it returns False (Don't skip).
+    
+    # Scene 2: last_scan exists and new Segments exist.
+    max_seg_date_mock = datetime(2023, 1, 2, 12, 0, 0, tzinfo=timezone.utc)
+    mock_db_session.query.return_value.scalar.return_value = max_seg_date_mock
+    
+    # Set activity last scan to OLDER
+    activity.last_segment_scan_timestamp = datetime(2023, 1, 1, 12, 0, 0, tzinfo=timezone.utc)
+    
+    # Check Logic
+    should_skip = (activity.last_segment_scan_timestamp >= max_seg_date_mock)
+    assert should_skip is False
+    
+    # Scene 3: last_scan is NEWER
+    activity.last_segment_scan_timestamp = datetime(2023, 1, 3, 12, 0, 0, tzinfo=timezone.utc)
+    should_skip = (activity.last_segment_scan_timestamp >= max_seg_date_mock)
+    assert should_skip is True