fix: replace TypeORM health check with Drizzle

[brentthomas248]

Closes #6

Summary:

• Remove the TypeORM health dependency and app wiring.
• Add a Drizzle-backed health indicator.
• Update health controller/module wiring and the smoke-test override.
• Add focused success/failure tests for the new health behavior.

Tests:

• npm test
• npm run build
• npm run lint (exits 0; existing warnings remain)
• npm run format:check
• git diff --check
• npm ls @nestjs/typeorm typeorm --depth=0 (empty; npm exits 1 because both packages are absent)
• rg -n "TypeOrm|TypeORM|typeorm|@nestjs/typeorm" package.json src (no matches)