Drop legacy pages, contexts, and dashboard widgets

Removes Dashboard / Transactions / Transfers pages, the section
configuration UI, the legacy useSettings hook, and the standalone
PrivacyContext/ThemeContext modules. Privacy/theme contexts now live
under src/contexts/ and the API helper / push-notifications module
move under src/lib/.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/lib/push-notifications.ts

@@ -0,0 +1,51 @@
+import api from './api';
+
+function urlBase64ToUint8Array(base64String: string): Uint8Array {
+  const padding = '='.repeat((4 - (base64String.length % 4)) % 4);
+  const base64 = (base64String + padding).replace(/-/g, '+').replace(/_/g, '/');
+  const rawData = window.atob(base64);
+  const outputArray = new Uint8Array(rawData.length);
+  for (let i = 0; i < rawData.length; ++i) {
+    outputArray[i] = rawData.charCodeAt(i);
+  }
+  return outputArray;
+}
+
+export async function subscribeToPush(): Promise<void> {
+  if (!('serviceWorker' in navigator) || !('PushManager' in window)) {
+    return;
+  }
+
+  const permission = await Notification.requestPermission();
+  if (permission !== 'granted') {
+    return;
+  }
+
+  try {
+    const { data } = await api.get<{ publicKey: string }>('/notifications/vapid-public-key');
+    const registration = await navigator.serviceWorker.ready;
+
+    const existing = await registration.pushManager.getSubscription();
+    if (existing) {
+      await sendSubscriptionToServer(existing);
+      return;
+    }
+
+    const subscription = await registration.pushManager.subscribe({
+      userVisibleOnly: true,
+      applicationServerKey: urlBase64ToUint8Array(data.publicKey),
+    });
+
+    await sendSubscriptionToServer(subscription);
+  } catch (err) {
+    console.warn('Push subscription failed:', err);
+  }
+}
+
+async function sendSubscriptionToServer(subscription: PushSubscription): Promise<void> {
+  const json = subscription.toJSON();
+  await api.post('/notifications/subscribe', {
+    endpoint: json.endpoint,
+    keys: json.keys,
+  });
+}