fix: inject duplicate-work context fetcher for testable lock/create_pr paths (#400)

Expose issue_duplicate_context_fetcher on the MCP server so lock_issue,
commit_files, and create_pr duplicate rechecks avoid live Gitea calls in
unit tests. Update affected test suites to patch the fetcher without
weakening duplicate-work gate assertions.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_agent_temp_artifacts.py

@@ -80,7 +80,10 @@ class TestIssueLockArtifactWarning(unittest.TestCase):
     def tearDown(self):
         self._env_patcher.stop()
 
-    @patch("mcp_server.api_get_all", return_value=[])
+    @patch(
+        "mcp_server.issue_duplicate_context_fetcher",
+        return_value=([], [], {"status": "not_claimed"}),
+    )
     @patch("mcp_server._auth", return_value="token x")
     @patch("mcp_server._resolve", return_value=("h", "o", "r"))
     @patch("mcp_server.ISSUE_LOCK_FILE", new_callable=lambda: tempfile.mktemp())