test: isolate CLI output capture with monkeypatch/redirect to fix stdout corruption in full suite runs (Issue #178)

- Replace raw patch("sys.stdout") and contextlib.redirect_stderr with pytest MonkeyPatch or contextlib redirect scoped to main calls in CLI tests (create_*, prs, python_cli, manage_labels, merge_pr, review_pr).
- Add regression tests in test_review_proofs.py for stdout/stderr remaining usable.
- Ensures normal pytest summary output without junitxml workaround; improves review validation reporting per #173.
- No behavior change to production code or gates.

Refs #178

tests/test_python_cli.py

@@ -4,6 +4,8 @@ All tests mock credentials and API requests so no real network calls are made.
 """
 import sys
 import unittest
+import io
+import contextlib
 from unittest.mock import patch, MagicMock
 
 # The modules under test live in the repo root
@@ -31,7 +33,8 @@ class TestCloseIssueCLI(unittest.TestCase):
     @patch("close_issue.api_request")
     @patch("close_issue.get_auth_header", return_value=FAKE_AUTH)
     def test_successful_close(self, _auth, mock_api):
-        rc = close_issue.main(["42"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = close_issue.main(["42"])
         self.assertEqual(rc, 0)
         mock_api.assert_called_once()
         url = mock_api.call_args[0][1]
@@ -69,7 +72,8 @@ class TestMarkIssueCLI(unittest.TestCase):
             [{"id": 101, "name": "status:in-progress"}],
             [{"name": "status:in-progress"}],
         ]
-        rc = mark_issue.main(["15", "start"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = mark_issue.main(["15", "start"])
         self.assertEqual(rc, 0)
         self.assertEqual(mock_api.call_count, 2)