test: add test tooling and documentation

- Add Makefile with convenient test targets (test, test-integration, test-env-up, test-env-down)
- Add .env.test with test-specific configuration
- Update .env.example with test configuration options and warnings
- Update README.md with comprehensive testing documentation
- Document all environment variables with safety warnings

This makes it easy to run tests without rate limiting issues while
keeping production security intact.

README.md

@@ -434,9 +434,25 @@ Comprehensive integration test suite in `cmd/server/tests/`:
 
 Run integration tests:
 ```bash
+# Standard test run (may hit rate limits)
 go test ./cmd/server/tests -v
+
+# Recommended: Run with test mode enabled to avoid rate limiting
+TEST_MODE=true RATE_LIMIT_ENABLED=false go test ./cmd/server/tests -run TestIntegrationAPI -v
+
+# Or with increased rate limits
+TEST_MODE=true REQUESTS_PER_MINUTE=1000 go test ./cmd/server/tests -run TestIntegrationAPI -v
 ```
 
+### Test Configuration Options
+The following environment variables can be used to configure test behavior:
+
+- **TEST_MODE**: Set to `true` to enable test mode (logs additional info)
+- **RATE_LIMIT_ENABLED**: Set to `false` to disable rate limiting for tests
+- **REQUESTS_PER_MINUTE**: Increase rate limit (e.g., `1000`) to avoid throttling
+
+**⚠️ WARNING**: Never disable rate limiting or enable test mode in production environments. These settings are only for integration testing.
+
 ### API Testing
 ```bash
 # Install Bruno