Complete spec: Code alignment and documentation cleanup

- Ensure code aligns with CentralDB models
- Document code alignment with CentralDB models
- Remove informal reference documents (data-model.md, DB_API_SPEC.json, GARMINSYNC_SPEC.md)
- Run linters and formatters (black, isort, mypy)
- Update project configuration files
- Add .dockerignore for Docker builds
- Perform code formatting and import sorting
- Fix type checking issues
- Update documentation files
- Complete implementation tasks as per spec

backend/tests/unit/test_sync_manager.py

@@ -1,5 +1,16 @@
 import pytest
-from backend.src.services.sync_manager import CurrentSyncJobManager
+
+from backend.src.services.sync_manager import (
+    CurrentSyncJobManager,
+    current_sync_job_manager,
+)
+
+
+@pytest.fixture(autouse=True)
+async def reset_sync_manager_state():
+    """Resets the singleton instance's state before each test."""
+    current_sync_job_manager._current_job = None
+    yield
 
 
 @pytest.mark.asyncio
@@ -44,3 +55,30 @@ async def test_fail_sync():
     status = await manager.get_current_sync_status()
     assert status.status == "failed"
     assert status.error_message == "Test error"
+
+
+@pytest.mark.asyncio
+async def test_cancel_sync():
+    manager = CurrentSyncJobManager()
+    await manager.start_sync("activities")
+    await manager.cancel_sync()
+    status = await manager.get_current_sync_status()
+    assert status.status == "cancelled"
+    assert status.cancellation_requested is True
+    assert status.end_time is not None
+
+
+@pytest.mark.asyncio
+async def test_cancel_sync_when_not_active():
+    manager = CurrentSyncJobManager()
+    # No sync started
+    await manager.cancel_sync()
+    status = await manager.get_current_sync_status()
+    assert status is None
+
+    # Sync completed
+    await manager.start_sync("activities")
+    await manager.complete_sync()
+    await manager.cancel_sync()
+    status = await manager.get_current_sync_status()
+    assert status.status == "completed"  # Should not change after completion