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/components/settings/AppearanceSettings.tsx

@@ -19,6 +19,8 @@ const THEME_LABELS: Record<string, string> = {
   "apple-light": "Apple Light",
   "intellij-light": "IntelliJ Light",
   canvas: "Canvas",
+  "orca-dark": "Orca Dark",
+  "orca-light": "Orca Light",
 };
 
 const MODES: { mode: ThemeMode; Icon: typeof Moon }[] = [

client/src/components/settings/__tests__/AppearanceSettings.test.tsx

@@ -26,7 +26,15 @@ describe("AppearanceSettings", () => {
       .map((b) => b.getAttribute("aria-label") ?? b.textContent);
     expect(pressed).toHaveLength(2); // both Default cards
     expect(screen.getByRole("radio", { name: /Dark/ })).toHaveAttribute("aria-checked", "true");
-    for (const name of ["Darcula", "Apple Dark", "Apple Light", "IntelliJ Light", "Canvas"]) {
+    for (const name of [
+      "Darcula",
+      "Apple Dark",
+      "Orca Dark",
+      "Apple Light",
+      "IntelliJ Light",
+      "Canvas",
+      "Orca Light",
+    ]) {
       expect(screen.getByText(name)).toBeInTheDocument();
     }
   });