docs: stop review_pr.py advertising CLI merge in docstring/help (#16)

Stale documentation only — no behavior change. The module docstring and the
--merge / --merge-method argparse help text no longer advertise a working CLI
merge. They now state CLI merge is disabled/fail-closed and that merge is
handled solely by the gated gitea_merge_pr MCP workflow (#16).

CLI merge remains disabled: --merge still fails closed with no API call, and
review_pr.py contains no /merge call. No MCP merge gate was changed.

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

review_pr.py

@@ -1,11 +1,14 @@
 #!/usr/bin/env python3
 """Review and sign-off on a Gitea pull request.
 
-Supports submitting a review (APPROVE, COMMENT, REQUEST_CHANGES) and optionally
-merging the pull request in one command.
+Submits a review (APPROVE, COMMENT, REQUEST_CHANGES). CLI merge is disabled:
+the `--merge` flag is retained only for compatibility and fails closed without
+making any API call. Merge is handled solely by the gated `gitea_merge_pr` MCP
+workflow (#16), which enforces identity/profile/eligibility, explicit
+confirmation, expected head SHA checking, and self-merge protection.
 
-Usage:
-    review_pr.py --pr-number 12 --event APPROVE --body "Approved and signed off" --merge
+Usage (review only):
+    review_pr.py --pr-number 12 --event APPROVE --body "Approved and signed off"
 """
 import os
 import sys
@@ -32,9 +35,11 @@ def main(argv=None):
                         help="Review event/action type (default: APPROVE).")
     parser.add_argument("--body", default="", help="Review body/comment text.")
     parser.add_argument("--body-file", help="Read review body from this file ('-' for stdin).")
-    parser.add_argument("--merge", action="store_true", help="Automatically merge the PR if approved.")
+    parser.add_argument("--merge", action="store_true",
+                        help="DISABLED — fails closed with no API call. CLI merge is not "
+                             "supported; use the gated gitea_merge_pr MCP workflow (#16).")
     parser.add_argument("--merge-method", choices=["merge", "squash", "rebase"], default="merge",
-                        help="Merge method/style to use if merging (default: merge).")
+                        help="Ignored — CLI merge is disabled (see --merge).")
     args = parser.parse_args(argv)
 
     # Fail closed: direct CLI merge is disabled (#16). LLM automations were