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/conftest.py

@@ -0,0 +1,26 @@
+import pytest
+from database import init_db, SessionLocal
+from models import Authorization
+
+
+@pytest.fixture(scope="session", autouse=True)
+def setup_database():
+    """Initialize DB tables and seed an Authorization row."""
+    init_db()
+    db = SessionLocal()
+    try:
+        existing = db.query(Authorization).first()
+        if existing is None:
+            auth = Authorization(
+                id="test-auth-1",
+                avatar_id="test-avatar-1",
+                target_type="user",
+                target_id="test-user-1",
+                target_name="Test User",
+                permissions=["read", "write"],
+                status="active",
+            )
+            db.add(auth)
+            db.commit()
+    finally:
+        db.close()