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/.env.test.example

@@ -0,0 +1,9 @@
+# WARNING: These are example test credentials for local integration testing.
+# Copy this file to .env.test and customize the values for your local environment.
+# NEVER use these credentials in any shared environment or commit .env.test to git.
+
+DATABASE_URL="postgresql://test:test@localhost:5432/test"
+ENCRYPTION_KEY="test-encryption-key-32-characters"
+JWT_SECRET="test-jwt-secret"
+INSTANCE_NAME="Test Instance"
+INSTANCE_URL="https://test.example.com"