refactor(watcher): split watcher.go into focused modules
- Create dispatcher.go for auth update queue management
- Create events.go for fsnotify event handling
- Create config_reload.go for hot-reload logic
- Create clients.go for client lifecycle management
- Simplify watcher.go to core coordinator (~150 lines)
- Maintain 100% API backward compatibility
- All tests passing with 72%+ coverage
hkfires