fix: Claude reviewer empty output, worktree isolation false positives, and input file access

- Add -p flag to _CLAUDE_REVIEW_ARGS so reviewer uses print mode (stdin→stdout)
  instead of interactive mode which conflicts with plan permission mode
- Copy input files (plan, checklist) into worktree .cross-eval-inputs/ so
  agents in plan mode can access them without escaping the sandbox
- Simplify _snapshot_repo_state to use only git diff HEAD + untracked hashes,
  eliminating false positives from staging state changes (git diff --cached)
  and git status index drift during long-running pipelines

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_runtime_misc.py

@@ -390,7 +390,7 @@ class TestPipelineHelpers(unittest.TestCase):
 
             snapshot = _snapshot_repo_state(repo)
 
-            self.assertIn("UNTRACKED scratch.txt", snapshot)
+            self.assertIn("UNTRACKED scratch.txt", snapshot["untracked"])
 
     def test_finalize_worktree_deletes_empty_branch(self) -> None:
         with tempfile.TemporaryDirectory() as tmpdir: