- Introduced a new `.env.test.example` file for integration test configuration.
- Added a `Makefile` to streamline test commands for unit and integration tests.
- Implemented an integration testing harness with support for PostgreSQL, MinIO, and Redis using testcontainers.
- Created a suite of integration tests covering health checks and user management functionalities.
- Enhanced CI workflow to include integration tests with necessary environment variables.
- Created a CI workflow in `.github/workflows/ci.yml` to run Go tests and verify database migrations.
- Added unit tests for the mail API in `internal/api/mail/handlers_test.go`, covering message listing, retrieval, sending, and label updating.
- Introduced a service interface for the mail handler in `internal/api/mail/service_iface.go`.
- Updated mail handler initialization to accept a service API in `internal/api/mail/handlers.go`.
- Implemented test authentication middleware for testing purposes in `internal/api/middleware/testauth.go`.
- Added various test cases for IMAP and SMTP functionalities, ensuring robust error handling and validation.
- Enhanced project documentation with checklist updates for testing and CI integration.
