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_prs.py

@@ -4,6 +4,8 @@ Mocks api_request and credentials.
 """
 import sys
 import unittest
+import io
+import contextlib
 from unittest.mock import patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
@@ -24,14 +26,16 @@ class TestListPRs(unittest.TestCase):
         mock_api.return_value = [
             {"number": 1, "title": "PR 1", "head": {"ref": "branch1"}, "base": {"ref": "main"}, "html_url": "http://url1", "mergeable": True}
         ]
-        rc = list_prs.main([])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = list_prs.main([])
         self.assertEqual(rc, 0)
         mock_api.assert_called_once()
 
     @patch("list_prs.api_request", return_value=[])
     @patch("list_prs.get_auth_header", return_value=FAKE_CREDS)
     def test_list_prs_empty(self, _auth, mock_api):
-        rc = list_prs.main(["--state", "closed"])
+        with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+            rc = list_prs.main(["--state", "closed"])
         self.assertEqual(rc, 0)
         mock_api.assert_called_once()