feat(ui): Orca Dark / Orca Light themes and notification sounds

Two optional named themes from Orca's neutral palette join the Appearance
picker (Orca Dark keeps a blue accent so white-on-accent buttons stay
legible; Orca Light's status colours are darkened to clear 4.5:1 on their
chips). A shown notification can play a sound — None (default), Chime, Pop
or Alert — chosen globally and per notification type in Settings →
Notifications; the WAVs are generated by scripts/gen-notification-sounds.js.

client/src/lib/notify.ts

@@ -2,10 +2,29 @@
  * @file Shows a browser notification — the single `notify()` both
  * `useNotifications` (live events) and Settings' "Send Test Notification"
  * button call, so the test proves the real delivery path and can report
- * where it actually landed instead of a bare fire-and-forget.
+ * where it actually landed instead of a bare fire-and-forget. `playSound`
+ * plays one of the generated `public/sounds/*.wav` (see
+ * `scripts/gen-notification-sounds.js`).
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
+import type { NotifSound } from "./notifPrefs";
+
+const audio = new Map<NotifSound, HTMLAudioElement>();
+
+/** Plays a notification sound from the start; "none" plays nothing. A browser
+ *  that refuses autoplay before a user gesture is left to refuse quietly. */
+export function playSound(kind: NotifSound): void {
+  if (kind === "none") return;
+  let el = audio.get(kind);
+  if (!el) {
+    el = new Audio(`/sounds/${kind}.wav`);
+    audio.set(kind, el);
+  }
+  el.currentTime = 0;
+  void el.play()?.catch(() => {});
+}
+
 export type NotifyVia = "native" | "push" | "local" | "blocked" | "none";
 
 export interface NotifyError {