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_manage_labels.py

@@ -2,9 +2,11 @@
 
 All API calls are mocked — no real network or keychain access.
 """
+import io
 import json
 import sys
 import unittest
+import contextlib
 from unittest.mock import MagicMock, call, patch
 
 sys.path.insert(0, str(__import__("pathlib").Path(__file__).resolve().parent.parent))
@@ -33,7 +35,8 @@ class TestLabelCreation(unittest.TestCase):
 
         # Patch sys.argv to avoid --dry
         with patch.object(sys, "argv", ["manage_labels.py"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         # The GET call happens, but no POST calls for label creation
         get_calls = [c for c in mock_api.call_args_list if c[0][0] == "GET"]
@@ -59,7 +62,8 @@ class TestLabelCreation(unittest.TestCase):
 
         mock_api.side_effect = side_effect
         with patch.object(sys, "argv", ["manage_labels.py"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         post_calls = [
             c for c in mock_api.call_args_list
@@ -79,7 +83,8 @@ class TestDryRun(unittest.TestCase):
         mock_api.return_value = []  # no existing labels
 
         with patch.object(sys, "argv", ["manage_labels.py", "--dry"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         # Only the GET call should be made, no POST or PUT
         for c in mock_api.call_args_list:
@@ -107,7 +112,8 @@ class TestLabelMapping(unittest.TestCase):
 
         mock_api.side_effect = side_effect
         with patch.object(sys, "argv", ["manage_labels.py"]):
-            manage_labels.main()
+            with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
+                manage_labels.main()
 
         put_calls = [c for c in mock_api.call_args_list if c[0][0] == "PUT"]
         self.assertEqual(len(put_calls), len(manage_labels.MAPPING))