Add login success/failure feedback message

Shows "Logged in successfully!" or "Login failed" after clicking
the managed mode Login button.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/components/Settings.svelte

@@ -257,15 +257,20 @@
 
   const MANAGED_SERVER_URL = "https://transcribe.shadowdao.com";
 
+  let loginMessage = $state("");
+
   async function handleManagedLogin() {
+    loginMessage = "";
     try {
       await backendStore.apiPost("/api/login", {
         email: managedEmail,
         password: managedPassword,
         server_url: remoteServerUrl || MANAGED_SERVER_URL,
       });
+      loginMessage = "Logged in successfully!";
     } catch (err) {
       console.error("Login failed:", err);
+      loginMessage = "Login failed. Check your email and password.";
     }
   }
 
@@ -504,6 +509,11 @@
             <div class="auth-buttons">
               <button onclick={handleManagedLogin}>Login</button>
             </div>
+            {#if loginMessage}
+              <p style="font-size: 12px; margin-top: 6px; color: {loginMessage.startsWith('Logged') ? 'var(--accent-green, #4CAF50)' : 'var(--accent-red, #f44336)'};">
+                {loginMessage}
+              </p>
+            {/if}
             <p style="font-size: 11px; color: var(--text-muted); margin-top: 8px;">
               Don't have an account? <a href="https://transcribe.shadowdao.com/register.html" target="_blank" rel="noopener" style="color: var(--accent-blue);">Sign up here</a>
             </p>