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/useNotifications.ts

@@ -54,8 +54,8 @@ import i18n from "../i18n";
 import { api } from "../lib/api";
 import { eventBus } from "../lib/eventBus";
 import { subscribeToPush } from "../lib/push";
-import { notify } from "../lib/notify";
-import { loadNotifPrefs } from "../lib/notifPrefs";
+import { notify, playSound } from "../lib/notify";
+import { loadNotifPrefs, soundFor, type NotifType } from "../lib/notifPrefs";
 import type { WSMessage, Session, Agent, DashboardEvent, Lane } from "../lib/types";
 
 /**
@@ -104,12 +104,20 @@ export function useNotifications() {
 
       const prefs = loadNotifPrefs();
       if (!prefs.enabled) return;
+      // A notification that was shown (pushed, native or local) plays its
+      // type's sound; one that reached nobody plays nothing.
+      const show = (type: NotifType, title: string, body: string, url?: string) =>
+        void notify(title, body, url).then((r) => {
+          if (r.via === "native" || r.via === "push" || r.via === "local")
+            playSound(soundFor(prefs, type));
+        });
 
       switch (msg.type) {
         case "session_created": {
           if (!prefs.onNewSession) return;
           const s = msg.data as Session;
-          notify(
+          show(
+            "onNewSession",
             i18n.t("errors:notifications.newSession"),
             s.name || `${i18n.t("errors:notifications.sessionDefault")}${s.id.slice(0, 8)}`,
             laneUrlForSession(s.id)
@@ -119,7 +127,8 @@ export function useNotifications() {
         case "session_updated": {
           const s = msg.data as Session;
           if (s.status === "error" && prefs.onSessionError) {
-            notify(
+            show(
+              "onSessionError",
               i18n.t("errors:notifications.sessionError"),
               s.name || `${i18n.t("errors:notifications.sessionDefault")}${s.id.slice(0, 8)}`,
               laneUrlForSession(s.id)
@@ -131,7 +140,8 @@ export function useNotifications() {
           if (!prefs.onSubagentSpawn) return;
           const a = msg.data as Agent;
           if (a.type === "subagent") {
-            notify(
+            show(
+              "onSubagentSpawn",
               i18n.t("errors:notifications.subagentSpawned"),
               a.name,
               laneUrlForSession(a.session_id)
@@ -148,19 +158,22 @@ export function useNotifications() {
           // `onSessionComplete` / nothing at all, so the one thing the user
           // actually waits for was either off by default or unswitchable.
           if (ev.event_type === "Notification" && prefs.onAwaitingInput) {
-            notify(
+            show(
+              "onAwaitingInput",
               i18n.t("errors:notifications.awaitingInput"),
               ev.summary || i18n.t("errors:notifications.defaultBody"),
               url
             );
           } else if (ev.event_type === "Stop" && prefs.onTurnComplete) {
-            notify(
+            show(
+              "onTurnComplete",
               i18n.t("errors:notifications.finishedResponding"),
               ev.summary || i18n.t("errors:notifications.readyForInput"),
               url
             );
           } else if (ev.event_type === "SessionEnd" && prefs.onSessionComplete) {
-            notify(
+            show(
+              "onSessionComplete",
               i18n.t("errors:notifications.sessionCompleted"),
               ev.summary || i18n.t("errors:notifications.sessionClosed"),
               url