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_create_pr.py

@@ -7,6 +7,7 @@ import io
 import json
 import sys
 import unittest
+import contextlib
 from unittest.mock import MagicMock, patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
@@ -34,7 +35,8 @@ class TestArgParsing(unittest.TestCase):
     @patch("create_pr.urllib.request.urlopen", return_value=_mock_urlopen())
     @patch("create_pr.get_credentials", return_value=FAKE_CREDS)
     def test_minimal_required_args(self, _cred, _url):
-        rc = create_pr.main(["--title", "PR Title", "--head", "feat/branch"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = create_pr.main(["--title", "PR Title", "--head", "feat/branch"])
         self.assertEqual(rc, 0)
 
     def test_missing_title_exits(self):