fix: complete mock move by removing root-level duplicates

The previous commit copied mocks to mocks/ but didn't delete
the originals. This removes the root-level mock_synapse.py and
mock-google-oidc/, updates path references in the mocks/ copies,
and adds config.yaml to .gitignore.

.gitignore

@@ -10,5 +10,9 @@ target
 .idea
 .nova
 
+# Local config (may contain secrets)
+config.yaml
+config.local.yaml
+
 # OS garbage
 .DS_Store