feat: Login-Formular merkt sich Benutzername

- Benutzername wird in localStorage gespeichert
- Beim nächsten Login automatisch ausgefüllt
- Verbessert UX für wiederkehrende Logins

src/client/components/login-form.tsx

@@ -1,4 +1,4 @@
-import { useState } from "react";
+import { useState, useEffect } from "react";
 import { useAuth } from "@/client/components/auth-provider";
 
 export function LoginForm() {
@@ -6,9 +6,27 @@ export function LoginForm() {
   const [password, setPassword] = useState("");
   const [error, setError] = useState("");
   const [isLoading, setIsLoading] = useState(false);
+  const [isInitialized, setIsInitialized] = useState(false);
   
   const { login } = useAuth();
 
+  // Load saved username from localStorage on mount
+  useEffect(() => {
+    const savedUsername = localStorage.getItem("loginForm_username");
+    if (savedUsername) setUsername(savedUsername);
+    setIsInitialized(true);
+  }, []);
+
+  // Save username to localStorage when it changes (after initial load)
+  useEffect(() => {
+    if (!isInitialized) return;
+    if (username) {
+      localStorage.setItem("loginForm_username", username);
+    } else {
+      localStorage.removeItem("loginForm_username");
+    }
+  }, [username, isInitialized]);
+
   const handleSubmit = async (e: React.FormEvent) => {
     e.preventDefault();
     setError("");