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/hooks/__tests__/useNotifications.test.ts

@@ -3,7 +3,8 @@
  * browser notification, and which preference gates each one. Covers issue #29:
  * "Claude needs confirmation" and "Claude finished a turn" must fire out of the
  * box once notifications are enabled, since those are the two moments the user
- * is the blocker.
+ * is the blocker. Also: a shown notification plays its type's sound, else the
+ * default one, and "none" plays nothing.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -104,6 +105,46 @@ describe("useNotifications", () => {
     expect(Notification).not.toHaveBeenCalled();
   });
 
+  it("plays the type's own sound, else the default, and nothing for none", async () => {
+    const played: string[] = [];
+    vi.spyOn(HTMLMediaElement.prototype, "play").mockImplementation(function (
+      this: HTMLMediaElement
+    ) {
+      played.push(this.src.split("/").pop()!);
+      return Promise.resolve();
+    });
+    // The hook's own lane list must read as a list, or a later event finds none.
+    fetchMock.mockImplementation(async (url: string) => ({
+      ok: true,
+      json: async () =>
+        url === "/api/push/send"
+          ? { ok: true, native: true, pushed: 1 }
+          : { lanes: [], counts: {} },
+    }));
+    enable({ sound: "chime", soundByType: { onTurnComplete: "pop", onAwaitingInput: "none" } });
+    renderHook(() => useNotifications());
+
+    emit("Stop", "Done");
+    await vi.waitFor(() => expect(played).toEqual(["pop.wav"]));
+    emit("Notification", "needs permission");
+    await vi.waitFor(() => expect(sentTitles()).toHaveLength(2));
+    await new Promise((r) => setTimeout(r, 20));
+    expect(played).toEqual(["pop.wav"]);
+
+    localStorage.setItem(
+      NOTIF_KEY,
+      JSON.stringify({
+        ...defaultNotifPrefs,
+        enabled: true,
+        sound: "chime",
+        onSessionComplete: true,
+      })
+    );
+    emit("SessionEnd", "Closed");
+    await vi.waitFor(() => expect(played).toEqual(["pop.wav", "chime.wav"]));
+    vi.restoreAllMocks();
+  });
+
   it("stays silent while notifications are disabled", async () => {
     renderHook(() => useNotifications());