fix(reviewer): close forbidden-git detection gaps via allowlist (#243)

Replace blocklist-based git mutation detection with fail-closed allowlist
semantics: any git command not matching the readonly set is forbidden.
Catches checkout HEAD --, checkout ., git switch variants, and uncommon
stash subcommands that bypassed the old regex.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_reviewer_worktree.py

@@ -65,6 +65,23 @@ class TestForbiddenGitCommands(unittest.TestCase):
         self.assertTrue(is_forbidden_reviewer_git_command("git reset --hard"))
         self.assertTrue(is_forbidden_reviewer_git_command("git clean -fd"))
 
+    def test_blocks_checkout_restore_and_switch_bypasses(self):
+        """Issue #243: blocklist gaps closed via readonly allowlist model."""
+        blocked = (
+            "git checkout HEAD -- review_proofs.py",
+            "git checkout prgs/master -- review_proofs.py",
+            "git checkout .",
+            "git switch -",
+            "git switch -C feat/other-branch",
+            "git switch master",
+            "git stash store",
+            "git stash branch wip-stash",
+        )
+        for cmd in blocked:
+            with self.subTest(cmd=cmd):
+                self.assertTrue(is_forbidden_reviewer_git_command(cmd))
+                self.assertFalse(is_readonly_reviewer_git_command(cmd))
+
     def test_allows_readonly_commands(self):
         for cmd in (
             "git fetch prgs master",