fix(tests): add endpoint URL to archived session seeds

The sessions table now enforces NOT NULL on endpoint_url, but the
test fixture omitted it when seeding archived sessions, causing
IntegrityError on all three test cases.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/test_archived_sessions_model_filter.py

@@ -51,7 +51,7 @@ def _seed(owner, *models):
         db.query(DbSession).delete()
         for m in models:
             db.add(DbSession(id=str(uuid.uuid4()), owner=owner, name=f"chat {m}",
-                             model=m, archived=True))
+                             endpoint_url="http://localhost", model=m, archived=True))
         db.commit()
     finally:
         db.close()