feat: add takeover fields to Authorization model

Add takeover_enabled, takeover_mode, and takeover_delay_seconds columns
to the Authorization model with a SQLite migration, and include them
in to_dict(). Test: test_takeover_model.py.

digital-avatar-app/backend/tests/test_takeover_model.py

@@ -0,0 +1,30 @@
+from database import SessionLocal
+from models import Authorization
+
+
+def test_authorization_takeover_fields():
+    db = SessionLocal()
+    try:
+        auth = db.query(Authorization).first()
+        assert auth is not None
+        # Check new fields exist and have default values
+        assert hasattr(auth, 'takeover_enabled')
+        assert hasattr(auth, 'takeover_mode')
+        assert hasattr(auth, 'takeover_delay_seconds')
+        assert auth.takeover_enabled == False
+        assert auth.takeover_mode == 'immediate'
+        assert auth.takeover_delay_seconds == 30
+    finally:
+        db.close()
+
+
+def test_authorization_to_dict_includes_takeover():
+    db = SessionLocal()
+    try:
+        auth = db.query(Authorization).first()
+        d = auth.to_dict()
+        assert 'takeoverEnabled' in d
+        assert 'takeoverMode' in d
+        assert 'takeoverDelaySeconds' in d
+    finally:
+        db.close()