fix(test): Fix DATABASE_URL environment setup for integration tests

Fixes integration test failures caused by missing DATABASE_URL environment variable.

Changes:
- Add dotenv as dev dependency to load .env.test in vitest setup
- Add .env.test to .gitignore to prevent committing test credentials
- Create .env.test.example with warning comments for documentation
- Add conditional test skipping when DATABASE_URL is not available
- Add DATABASE_URL format validation in vitest setup
- Add error handling to test cleanup to prevent silent failures
- Remove filesystem path disclosure from error messages

The fix allows integration tests to:
- Load DATABASE_URL from .env.test locally for developers with database setup
- Skip gracefully if DATABASE_URL is not available (no database running)
- Connect to postgres service in CI where DATABASE_URL is explicitly provided

Tests affected: auth-rls.integration.spec.ts and other integration tests
requiring real database connections.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/package.json

@@ -89,6 +89,7 @@
     "@types/sanitize-html": "^2.16.0",
     "@types/supertest": "^6.0.3",
     "@vitest/coverage-v8": "^4.0.18",
+    "dotenv": "^17.2.4",
     "express": "^5.2.1",
     "prisma": "^6.19.2",
     "supertest": "^7.2.2",