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>

.gitignore

@@ -30,6 +30,7 @@ Thumbs.db
 # Environment
 .env
 .env.local
+.env.test
 .env.development.local
 .env.test.local
 .env.production.local