fix: close ungated CLI merge bypasses in review_pr.py and merge_pr.py (#16)

Reviewer found the MCP merge surface is gated but two local CLI scripts remain
ungated merge paths that LLM automations in this project have been using.
Close them (Option B — minimal safe fix; full gated CLI merge left to a
follow-up):

- review_pr.py: `--merge` now fails closed BEFORE any API call with a clear
  message directing callers to the gated `gitea_merge_pr` MCP workflow. The
  review-only path is unchanged. The merge execution block was removed.
- merge_pr.py: main() is now a fail-closed no-op — reads no credentials and
  makes no merge API call; prints that merge is only available via the gated
  workflow.
- README: the `review_pr.py` row and Quick Examples no longer advertise a CLI
  `--merge` path; added an audit-logging clarification that #16 returns
  structured gate/merge results but does not add durable audit logging, which
  is tracked by #18.

Tests updated/added:
- test_review_pr.py: `--merge` fails closed with no API call; message points to
  the gated workflow.
- test_merge_pr.py: merge fails closed with no API call, even with
  --force/--do/--title/--message; message points to the gated workflow.
- test_mcp_server.py: README no longer advertises the ungated CLI merge example.

The gated MCP `gitea_merge_pr` is unchanged and still gated; `gitea_review_pr`
still fails closed on merge=True; `gitea_submit_pr_review` still cannot merge.
No secrets, auth headers, raw env, or credential paths are exposed. No
Jenkins/Ops/GlitchTip/Release/deploy/CI behavior added. #17/#18 not started.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_mcp_server.py

@@ -602,6 +602,17 @@ class TestNoUngatedMergePath(unittest.TestCase):
         merge_src = inspect.getsource(mcp_server.gitea_merge_pr)
         self.assertIn("/merge\"", merge_src)
 
+    def test_readme_no_longer_advertises_ungated_cli_merge(self):
+        import pathlib
+        readme = (pathlib.Path(__file__).resolve().parent.parent
+                  / "README.md").read_text(encoding="utf-8")
+        # The old ungated example command must be gone.
+        self.assertNotIn('--body "Approved" --merge', readme)
+        # And the gated messaging / audit deferral must be present.
+        self.assertIn("disabled", readme.lower())
+        self.assertIn("gitea_merge_pr", readme)
+        self.assertIn("#18", readme)
+
 
 # ---------------------------------------------------------------------------
 # Review PR