Stop the test suite from truncating whatever DB it's pointed at

Summary

• Added backend/src/config/database.ts with a resolveDatabaseURL() helper which returns DATABASE_URL_TEST under NODE_ENV=test or else DATABASE_URL.
• Routed all three DB connections through it, the drizzle db in index.ts (every controller), the pg pool in db.ts (the test query runner), and drizzle.config.ts.
• Added jest.setup.ts and switched jest.config.ts setupFiles to it, forcing NODE_ENV=test so the resolver and guard always see a test environment.
• Guarded resetTables in testUtils.ts: refuses to run unless NODE_ENV=test and DATABASE_URL_TEST is set.
• Added resetTables.test.ts.
• Added db:push:test to backend's package.json.
• Tests now use a dedicated album-reviews-test-db instead of the live dev DB, so a normal pnpm test no longer wipes real data.

 PASS  src/__tests__/resetTables.test.ts
 PASS  src/__tests__/artistLeaderboard.test.ts
 PASS  src/__tests__/scoreCalculation.test.ts
 PASS  src/__tests__/scoreIntegration.test.ts
 PASS  src/__tests__/album.test.ts
 PASS  src/__tests__/genre.test.ts
 PASS  src/__tests__/stats.test.ts
 PASS  src/__tests__/artist.test.ts
 PASS  src/__tests__/track.test.ts
 PASS  src/__tests__/bookmarks.test.ts
 PASS  src/__tests__/spotify.test.ts
 PASS  src/__tests__/unratedArtist.test.ts
 PASS  src/__tests__/auth.test.ts

Test Suites: 13 passed, 13 total
Tests:       65 passed, 65 total
Snapshots:   0 total
Time:        30.299 s
Ran all test suites.