Fix all compile warnings in frontend and backend

Removed unused imports, fields, methods, and structs that were generating warnings during compilation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/src/lib.rs

@@ -1,14 +1,10 @@
 use axum::{
-    extract::State,
-    http::StatusCode,
     response::Json,
     routing::{get, post},
     Router,
 };
-use serde::{Deserialize, Serialize};
-use sqlx::{sqlite::SqlitePool, Row};
+use sqlx::sqlite::SqlitePool;
 use tower_http::cors::{CorsLayer, Any};
-use uuid::Uuid;
 use std::sync::Arc;
 
 mod auth;
@@ -16,7 +12,6 @@ mod models;
 mod handlers;
 
 use auth::AuthService;
-use models::{LoginRequest, RegisterRequest, AuthResponse, ApiError};
 
 #[derive(Clone)]
 pub struct AppState {