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/handlers.rs

@@ -1,17 +1,12 @@
 use axum::{
-    extract::{Query, State},
-    http::{HeaderMap, StatusCode},
+    extract::State,
+    http::HeaderMap,
     response::Json,
 };
-use serde::Deserialize;
 use std::sync::Arc;
 
 use crate::{AppState, models::{LoginRequest, RegisterRequest, AuthResponse, ApiError}};
 
-#[derive(Deserialize)]
-pub struct VerifyQuery {
-    pub token: String,
-}
 
 pub async fn register(
     State(state): State<Arc<AppState>>,