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/__tests__/notifPrefs.test.ts

@@ -0,0 +1,45 @@
+/**
+ * @file notifPrefs.test.ts
+ * @description Notification prefs: the defaults (sound "none"), a blob stored
+ * before sounds existed loading with sound "none", `soundByType` surviving a
+ * save/load round trip, and `soundFor` preferring a type's override.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { beforeEach, describe, expect, it } from "vitest";
+import {
+  NOTIF_KEY,
+  defaultNotifPrefs,
+  loadNotifPrefs,
+  saveNotifPrefs,
+  soundFor,
+} from "../notifPrefs";
+
+beforeEach(() => localStorage.clear());
+
+describe("notifPrefs", () => {
+  it("defaults to no sound", () => {
+    expect(loadNotifPrefs()).toEqual(defaultNotifPrefs);
+    expect(defaultNotifPrefs.sound).toBe("none");
+  });
+
+  it("loads a blob written before sounds existed with sound none", () => {
+    localStorage.setItem(NOTIF_KEY, JSON.stringify({ enabled: true, onNewSession: true }));
+    const prefs = loadNotifPrefs();
+    expect(prefs.sound).toBe("none");
+    expect(prefs.enabled).toBe(true);
+    expect(prefs.soundByType).toBeUndefined();
+  });
+
+  it("round-trips soundByType and resolves a type's sound", () => {
+    saveNotifPrefs({
+      ...defaultNotifPrefs,
+      sound: "chime",
+      soundByType: { onTurnComplete: "pop" },
+    });
+    const prefs = loadNotifPrefs();
+    expect(prefs.soundByType).toEqual({ onTurnComplete: "pop" });
+    expect(soundFor(prefs, "onTurnComplete")).toBe("pop");
+    expect(soundFor(prefs, "onSessionError")).toBe("chime");
+  });
+});

client/src/lib/notifPrefs.ts

@@ -3,12 +3,26 @@
  * the defaults, and the `localStorage` read/write. Settings (which edits them)
  * and `useNotifications` (which obeys them) both import from here; they used to
  * carry private copies, so adding a notification type meant editing the same
- * literal twice and a miss went unnoticed until a toggle did nothing.
+ * literal twice and a miss went unnoticed until a toggle did nothing. A
+ * shown notification also plays a sound: `sound` is the default, and
+ * `soundByType` may override it per notification type (`soundFor`).
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
 export const NOTIF_KEY = "agent-monitor-notifications";
 
+export const NOTIF_SOUNDS = ["none", "chime", "pop", "alert"] as const;
+export type NotifSound = (typeof NOTIF_SOUNDS)[number];
+
+/** The per-type flags — every key a notification is gated on. */
+export type NotifType =
+  | "onNewSession"
+  | "onSessionError"
+  | "onAwaitingInput"
+  | "onTurnComplete"
+  | "onSessionComplete"
+  | "onSubagentSpawn";
+
 export interface NotifPrefs {
   /** Master switch; when false no notification fires, whatever the flags say. */
   enabled: boolean;
@@ -21,6 +35,9 @@ export interface NotifPrefs {
   /** The whole session closed (`SessionEnd`), not just one turn. */
   onSessionComplete: boolean;
   onSubagentSpawn: boolean;
+  /** The sound a shown notification plays, unless its type overrides it. */
+  sound: NotifSound;
+  soundByType?: Partial<Record<NotifType, NotifSound>>;
 }
 
 // The two "Claude is waiting for you" types default ON: they are the reason
@@ -34,8 +51,14 @@ export const defaultNotifPrefs: NotifPrefs = {
   onTurnComplete: true,
   onSessionComplete: false,
   onSubagentSpawn: false,
+  sound: "none",
 };
 
+/** The sound for one notification type: its override, else the default. */
+export function soundFor(prefs: NotifPrefs, type: NotifType): NotifSound {
+  return prefs.soundByType?.[type] ?? prefs.sound;
+}
+
 /** Reads prefs, merged over the defaults so a stored blob written by an older
  * build (missing the newer flags) still yields a complete object. */
 export function loadNotifPrefs(): NotifPrefs {

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 {