fix: enforce audit timeout across retries

[00200200]

Summary

Enforce claudecode-timeout as a deadline for the complete Claude audit, including retry attempts.

Previously, each of the three subprocess attempts received the full configured timeout, so a stalled run could last up to three times longer than requested. The runner now tracks one monotonic deadline, passes only the remaining time to each subprocess, and bounds retry backoff to that remaining budget.

Fixes #124.

Validation

• pytest -q claudecode (174 passed)
• python3 -m py_compile claudecode/github_action_audit.py claudecode/test_claude_runner.py
• git diff --check