Introduces Discord OAuth2 integration for account association and login, including new routes for linking, unlinking, and authenticating via Discord. Adds supporting services, repositories, and schema validation for the OAuth2 flow. Refactors database schema and queries for consistency, and updates dependencies to include required OAuth2 libraries.
Add environment example, update .gitignore, and switch license to AGPL v3. Introduce error handling classes, ESLint config, and main modules for database, logging, certificate management, and utility functions. Add authentication routes, schemas, and service layer for a modular REST API. Update README and set up repository structure for further development.
