Implements graceful shutdown with broadcast channels and proper timeout handling
for scraper workers, scheduler, bot service, and status update tasks. Introduces
centralized shutdown utilities and improves service manager to handle parallel
shutdown with per-service timeouts instead of shared timeout budgets.
Key changes:
- Add utils module with shutdown helper functions
- Update ScraperService to return errors on shutdown failures
- Refactor scheduler with cancellable work tasks and 5s grace period
- Extract worker shutdown logic into helper methods for clarity
- Add broadcast channel shutdown support to BotService and status task
- Improve ServiceManager to shutdown services in parallel with individual timeouts
