fix: Correct syntax error when shutdown called before BG service is running

[jsantell]

Occurs when running bg worker in prod. TBD on what is actually terminating the server to cause this

   at �[0m�[1m�[3mshutdown�[0m (�[0m�[36mfile:///tmp/deno-compile-bg-charm-service/packages/background-charm-service/src/main.ts�[0m:�[0m�[33m44�[0m:�[0m�[33m15�[0m)
   service.stop().then(() => {
�[0m�[1m�[31merror�[0m: Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'then')

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Summary by cubic

Fixes a crash during shutdown when the background service isn’t running by making stop() always return a Promise and by binding signal handlers to a service-aware shutdown function. Prevents the TypeError and ensures graceful exits in production.

• Bug Fixes
  • stop() now returns a Promise in all cases (returns Promise.resolve([]) when not running), avoiding .then on undefined.
  • Reworked shutdown to capture the service (shutdown(service)) for SIGINT/SIGTERM, removing the ts-ignore and ensuring consistent behavior.

[cubic-dev-ai]

No issues found across 2 files