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/lib/api/notifications.ts

@@ -71,3 +71,56 @@ export function badgeLabel(count: number): string {
   if (count <= 0) return '';
   return count > 9 ? '9+' : String(count);
 }
+
+// Per-user settings: which channels each kind reaches. Kinds the user cannot
+// receive (admin kinds, for a non-admin) are not listed at all.
+export type NotificationKindSetting = {
+  kind: string;
+  admin_only: boolean;
+  inbox: boolean;
+  phone: boolean;
+  email: boolean;
+};
+
+export type NotificationChannel = 'inbox' | 'phone' | 'email';
+
+export type NotificationSettings = {
+  kinds: NotificationKindSetting[];
+  email_available: boolean;
+  email_unavailable_reason?: 'no_address' | 'smtp_not_configured';
+};
+
+export type NotificationSettingChange = { kind: string } & Partial<Record<NotificationChannel, boolean>>;
+
+export async function getNotificationSettings(): Promise<NotificationSettings> {
+  return api.get<NotificationSettings>('/api/me/notification-settings');
+}
+
+// Partial: only what the user touched, so two quick toggles on different rows
+// cannot overwrite each other on the server.
+export async function putNotificationSettings(
+  changes: NotificationSettingChange[]
+): Promise<NotificationSettings> {
+  return api.put<NotificationSettings>('/api/me/notification-settings', { kinds: changes });
+}
+
+export function createNotificationSettingsQuery() {
+  return createQuery({
+    queryKey: qk.notificationSettings(),
+    queryFn: getNotificationSettings,
+    staleTime: 60_000
+  });
+}
+
+/** Short row labels, menu-style (rule 188). Unknown kinds show their key. */
+export const NOTIFICATION_KIND_LABELS: Record<string, string> = {
+  request_approved: 'Request approved',
+  request_rejected: 'Request declined',
+  request_completed: 'New music arrived',
+  request_pending: 'Requests to review',
+  quarantine_flagged: 'Tracks flagged',
+  scan_failed: 'Library scan failed',
+  tracks_missing: 'Tracks gone missing',
+  duplicates_found: 'Duplicates to review',
+  playback_errors: 'Playback errors'
+};