- 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.
- Added rate limiting for outbound email sends to prevent abuse, implemented in `internal/api/mail/sendguard`.
- Introduced idempotency key support for email sending to avoid duplicate submissions.
- Enhanced attachment handling with new limits and validation in `internal/api/mail/limits`.
- Updated outbox processing to include retry logic and circuit breaker for SMTP failures.
- Improved HTML sanitization for email content to enhance security.
- Added unit tests for new features, ensuring robust functionality and error handling.
- Updated configuration options in `.env.example` for new mail settings.
- Introduced health checks for Nextcloud, Immich, and Jitsi in the .env.example file.
- Implemented Prometheus metrics for HTTP requests, IMAP sync, outbox processing, and webhook executions.
- Added Grafana configuration files for dashboards and data sources.
- Updated Docker Compose to include Prometheus and Grafana services.
- Enhanced logging middleware to include request IDs and metrics tracking.
- Created health checker for monitoring database and external service statuses.
- Updated README with observability setup instructions and service URLs.
