fix: prevent launchd crash loop when dist/index.js is missing

[kianwoon]

Summary

• Replace KeepAlive: true with KeepAlive: { PathState: { dist/index.js: true } } in the launchd plist
• launchd now only restarts the daemon when the entry script actually exists on disk
• Prevents the infinite crash loop that occurs when tsup cleans dist/ during a rebuild
• When dist/index.js reappears after build, launchd automatically starts the daemon

Root cause

The crash happens before any of our code runs — Node's module loader fails with MODULE_NOT_FOUND when dist/index.js is missing. Since KeepAlive: true unconditionally restarts, this creates a tight crash loop (9 crashes observed in production).

Test plan

• TypeScript compiles cleanly (npx tsc --noEmit)
• All 22 daemon tests pass
• Build succeeds (npm run build)
• Verified plist template contains PathState instead of KeepAlive: true
• Manual: delete dist/index.js, stop daemon → launchd should NOT restart
• Manual: recreate dist/index.js → launchd should auto-start

Closes #216