Fix custom element WorkerService to match init() refactor

[zhaoyuheng200]

Summary

• The custom_element/worker_service.ts (used via fileReplacements in angular.json during the custom_element build) was not updated when 49aa6a8 refactored WorkerService to use a lazy init() method instead of constructor initialization.
• This causes ng build custom_element to fail with TS2339: Property 'init' does not exist on type 'WorkerService', which blocks npm package builds.

Test plan

• Run ng build custom_element — should succeed without TS errors
• Run npm run build-npm — should produce the full npm package in custom_element_npm/dist/

[sealuck]

Confirmed this still reproduces on current upstream main at 202934b5caaa057f7150240e22d613214cb8c543:

TS2339: Property init does not exist on type WorkerService.
src/components/visualizer/app_service.ts:1114

I reproduced it with npx ng build custom_element in a clean worktree. Applying this PR lifecycle-compatible implementation makes the custom-element production build succeed. The init() recreation is also important when an existing visualizer receives a new graphCollections input, because setupWorker() registers a new message listener on each reinitialization.