Task #389: Notification sounds + vibration with per-user customization

- DB: 7 new user prefs (sound per slot, per-type toggles, vibration, mute, volume).
- API: PATCH /auth/me/notification-preferences with whitelisted partial update,
  integer guard for volume, and hydrated AuthUser response. AuthUser now exposes
  the 7 new fields.
- Frontend: Web Audio synth library (8 sounds), settings popover with global
  mute/vibration/volume/per-type toggles, slot tabs, sound preview buttons,
  shift+click on bell for quick mute. Concurrency-safe optimistic updates with
  monotonic seq counter. RTL-correct toggle knob transforms.
- Socket hook plays sound on notification_created (orders/meetings only) when
  tab is hidden, respecting global mute and per-type toggles.
- Audio unlock hook mounted globally to satisfy autoplay restrictions.
- AR/EN translations added.

Pre-existing TS errors in executive-meetings.ts (font_settings) and pre-existing
test failures in test workflow are unrelated to this task.

artifacts/tx-os/src/pages/home.tsx

@@ -65,6 +65,7 @@ import {
   type HomeClockSize,
 } from "@/components/clock";
 import { ClockStylePicker } from "@/components/clock-style-picker";
+import { NotificationSettingsPicker } from "@/components/notification-settings";
 
 type IconName = keyof typeof LucideIcons;
 function isIconName(x: string): x is IconName {
@@ -495,6 +496,7 @@ export default function HomePage() {
             currentStyle={user?.clockStyle ?? null}
             currentHour12={user?.clockHour12 ?? null}
           />
+          <NotificationSettingsPicker />
           <button
             onClick={toggleLanguage}
             aria-label="Toggle language"