fix: patch redis_client in test classes to match new Redis guards

The redis_client None guards added in the previous commit caused 9
test failures because redis_client is None in the test environment.

Fix: added @patch('routes.playground.indexing.redis_client', MagicMock())
to TestIndexEndpoint, TestSessionConflict, and TestStatusEndpoint.
TestStatusEndpoint uses MagicMock(get=MagicMock(return_value=None))
so test_job_not_found_returns_404 exercises the real AnonymousIndexingJob
code path (redis.get returns None -> job not found -> 404).

289 tests pass locally. Verified before committing.

Author: DevanshuNEU

backend/tests/test_anonymous_indexing.py

@@ -262,6 +262,7 @@ def test_job_stats_to_dict(self):
 
 # ENDPOINT TESTS (Integration)
 
+@patch('routes.playground.indexing.redis_client', MagicMock())
 class TestIndexEndpoint:
     """Integration tests for POST /playground/index."""
 
@@ -420,6 +421,7 @@ def test_github_rate_limit_returns_429(self, mock_metadata, client):
 
 # SESSION CONFLICT TESTS
 
+@patch('routes.playground.indexing.redis_client', MagicMock())
 class TestSessionConflict:
     """Tests for session-already-has-repo behavior."""
 
@@ -504,6 +506,7 @@ def test_expired_repo_allows_new_indexing(
 
 # STATUS ENDPOINT TESTS (GET /playground/index/{job_id})
 
+@patch('routes.playground.indexing.redis_client', MagicMock(get=MagicMock(return_value=None)))
 class TestStatusEndpoint:
     """Tests for GET /playground/index/{job_id} status endpoint."""