Fix development production build and migration startup

[kevinwmerritt]

Summary

• use NodeJS.Timeout for scheduled interval handles so the production TypeScript build accepts clearInterval
• give AddExternalIdToContacts1750299580000 an explicit migration name so TypeORM can identify it after production minification

Why

The packaged development build currently fails in two places:

1. TypeScript rejects NodeJS.Timer when it is passed to clearInterval with the current locked typings.

2. When upgrading an existing server database, the production-minified contact migration has the runtime class name t. TypeORM requires migration names to end in a 13-digit timestamp and aborts startup with:

   t migration name is wrong. Migration class name should have a JavaScript timestamp appended.

The older migrations already define an explicit name property for this reason.

Verification

• ESLint passes for both changed files.
• npm run build --workspace @bluebubbles/server succeeds.
• A packaged ARM64 build starts successfully against an existing BlueBubbles 1.9.9 configuration database on macOS 15.7.7.

[jattree]

Confirming this fixes startup of a packaged development build on macOS 26.6.2 (Tahoe, 25G83), Apple Silicon (M2).

Without it I hit both problems described here. The TypeScript build failed on clearInterval(this.handle) in ScheduledService.ts. After working around that, the packaged app started once on a fresh install (no config.db, so synchronize is used). Every later launch hung at Initializing server database.... Running the binary with its console captured showed the swallowed rejection:

TypeORMError: t migration name is wrong. Migration class name should have a JavaScript timestamp appended.
    at MigrationExecutor.getMigrations (.../typeorm/migration/MigrationExecutor.js:415:55)

With the same two changes as this PR (NodeJS.Timeout, and name = "AddExternalIdToContacts1750299580000"), the build succeeds. The app then starts normally on repeated launches against the existing database, with HTTP service up and iMessage listeners running.

Build details: development @ e2a5bf6 plus #832, Node 20.11.1, electron-builder arm64 target.