🐛 fix(thirdparty): use awesome master ref

Point codebase-migrate at the actual awesome-codex-skills master branch while keeping the whole-repo clone plus include_skill_dirs sync model.

Add a manifest assertion so the ref does not regress to main.

tests/test_thirdparty_skills_pipeline.py

@@ -101,6 +101,11 @@ class ThirdpartySkillsPipelineTests(unittest.TestCase):
         migrate = next(
             item for item in data["sources"] if item["id"] == "codebase-migrate"
         )
+        self.assertEqual(
+            migrate["upstream_repo"],
+            "https://github.com/ComposioHQ/awesome-codex-skills.git",
+        )
+        self.assertEqual(migrate["upstream_ref"], "master")
         self.assertEqual(migrate["sync_mode"], "copy_skill_dirs")
         self.assertEqual(migrate["snapshot_dir"], "awesome-codex-skills")
         self.assertEqual(migrate["skills_subdir"], ".")