feat(web): notification settings per kind and channel (#5345, web half)

- A Notifications section on Settings has a row per kind and a toggle
  each for Inbox, Phone and Email. Labels are short, menu-style.
- Admin kinds sit under "Library health", for admins only.
- Toggles are optimistic and send only the kind and channel touched. A
  failed save reverts unless something newer has happened (snippet
  #5106's generation counter).
- With the inbox off, phone and email are disabled: they ride on it.
- When email isn't usable, one line says why. With no address it links
  to the profile. With no SMTP an admin gets a link to Integrations and a
  listener is simply told. Saving the profile refreshes the settings so
  the line clears.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/routes/settings/Appearance.test.ts

@@ -25,6 +25,19 @@ vi.mock('$lib/api/listenbrainz', () => {
   };
 });
 
+// The Notifications section has its own tests (NotificationSettings.test.ts);
+// here it only needs a settled query so the page renders.
+vi.mock('$lib/api/notifications', async (importOriginal) => {
+  const mod = await importOriginal<typeof import('$lib/api/notifications')>();
+  const { mockQuery } = await import('../../test-utils/query');
+  return {
+    ...mod,
+    createNotificationSettingsQuery: () =>
+      mockQuery({ data: { kinds: [], email_available: true } }),
+    putNotificationSettings: vi.fn()
+  };
+});
+
 // The Volume leveling setting loads on mount; keep it off the network.
 vi.mock('$lib/api/normalization', async (importOriginal) => {
   const mod = await importOriginal<typeof import('$lib/api/normalization')>();