Add initial backend structure and configuration files

Commit notes

- Created `.gitignore` to exclude build artifacts, environment files, and logs. - Added `biome.json` for project configuration and linting rules. - Introduced `bun.lock` for dependency management. - Set up `bunfig.toml` for installation and test configurations. - Implemented `drizzle.config.ts` for database schema management. - Created example environment file `env.example` for configuration reference. - Established `package.json` with project dependencies and scripts. - Configured TypeScript settings in `tsconfig.json`. - Developed initial server setup in `src/index.ts` with routing and middleware. - Added audio processing utilities in `src/audio/ffmpeg.ts`. - Implemented authentication and user management in `src/auth` directory. - Set up database schema in `src/db/schema.ts` and connection in `src/db/index.ts`. - Created routes for user authentication, sample management, and project handling. - Added utility functions for slug generation and file size formatting.

This commit lays the foundation for the backend API, focusing on configuration, routing, and initial feature implementation.