Add Copilot proxy support and bootstrap flow

[lbx154]

Summary

• add Copilot proxy integration for CLI, daemon, and child Codex runs
• auto-detect proxy checkouts and support managed bootstrap into ~/.argusbot/tools/copilot-proxy
• make argusbot init / argusbot-setup easier by removing the need for --copilot-proxy-dir in common cases
• add copilot model preset, docs, and regression tests

Verification

• python -m compileall -q codex_autoloop tests
• PYTHONPATH=/home/v-boxiuli/ArgusBot /tmp/argusbot-review-venv/bin/python -m pytest -q tests
• 188 passed, 1 warning