Add tracked local integration pre-push hook

[RobertTLange]

What changed

• Added an opt-in real-agent local integration suite covering all six Headless backends, output modes, native sessions, tmux sessions, Docker, and Modal.
• Added a tracked .githooks/pre-push hook that blocks pushes unless the local integration suite passes.
• Added package scripts for installing the hook and running the local integration suite while keeping it out of npm test and npm run check.

Why

The full real-agent integration suite should be available and enforced locally before push, without making normal unit checks depend on authenticated providers, Docker, or Modal.

How to test

• npm run hooks:install
• npm run check
• npm run test:integration:local

Verification

• npm run hooks:install
• npm run check: passed, 151 tests
• git push with enabled pre-push hook: passed npm run test:integration:local, 7/7 tests including Docker and Modal