feat: implement authentication system

- Add auth.rs module with session management
- Implement login/logout/verify API endpoints
- Add authentication middleware
- Protect /api/v2/tree endpoint
- Default demo user (username: demo, password: demo123)
- Token-based auth with 24-hour expiration
- bcrypt password hashing

src/lib.rs

@@ -1,4 +1,5 @@
 pub mod audio;
+pub mod auth;
 pub mod command;
 pub mod filetree;
 pub mod render;