Handle binary harness judge targets

[fazpu]

Summary

• Render binary harness_judge target files as deterministic metadata instead of prompt content
• Keep text target rendering and truncation behavior unchanged
• Add a regression test proving NUL-containing targets do not place embedded NUL bytes in subprocess argv

Checks

• uv run ruff check src tests
• uv run pyright
• uv run pytest tests/test_harness_judge.py tests/test_harness_judge_binary_targets.py -q
• uv run pytest -q

Note: the local working tree also contains pre-existing unstaged gpt-5.5 model-update edits. They were preserved and are not included in this PR commit.