refactor: convert bin and stop hook to TypeScript, run via tsx

- bin/setup.mjs → bin/setup.ts with proper types (HarnessDef, CheckResult)
- src/bridges/codex/stop_hook.py → stop_hook.ts, uses core types
- All bridge execution uses npx tsx (or bun if available)
- No more Python dependency for Codex hook
- All configs reference: npx agent-bus bridge <id>
- Add tsx as devDependency

Author: Mearman