Improve login input fields for better UX

Removed default email and password placeholders for security and replaced them with empty values. Added placeholders and proper `autoComplete` attributes to enhance user experience and browser compatibility.

frontend/src/pages/LoginPage.jsx

@@ -5,8 +5,8 @@ import { useAuth } from "../state";
 export function LoginPage() {
   const { login } = useAuth();
   const navigate = useNavigate();
-  const [email, setEmail] = useState("admin@example.com");
-  const [password, setPassword] = useState("ChangeMe123!");
+  const [email, setEmail] = useState("");
+  const [password, setPassword] = useState("");
   const [error, setError] = useState("");
   const [loading, setLoading] = useState(false);
 
@@ -29,9 +29,21 @@ export function LoginPage() {
       <form className="card login-card" onSubmit={submit}>
         <h2>Login</h2>
         <label>Email</label>
-        <input value={email} onChange={(e) => setEmail(e.target.value)} />
+        <input
+          type="email"
+          placeholder="E-Mail"
+          value={email}
+          onChange={(e) => setEmail(e.target.value)}
+          autoComplete="username"
+        />
         <label>Passwort</label>
-        <input type="password" value={password} onChange={(e) => setPassword(e.target.value)} />
+        <input
+          type="password"
+          placeholder="Password"
+          value={password}
+          onChange={(e) => setPassword(e.target.value)}
+          autoComplete="current-password"
+        />
         {error && <p className="error">{error}</p>}
         <button disabled={loading}>{loading ? "Bitte warten..." : "Einloggen"}</button>
       </form>