feat(m5a): channel manager, tabbed settings panel, per-user sync status

Backend: /api/channels (list + PATCH priority/hidden + attach/detach user tags),
user-tag CRUD on /api/tags, /api/sync/my-status (per-user channel sync counts).
Frontend: feed|channels page nav (URL-synced) from the account menu; a slide-in
tabbed Settings panel (Appearance, Notifications=6b sound+duration, Sync status +
actions + admin pause/resume, Account); a channel manager with priority, hide,
per-channel user tags, sync badges and 'view in feed'. Notifications now honor the
configurable sound + auto-dismiss settings.

frontend/src/lib/notifications.ts

@@ -44,10 +44,58 @@ export interface NotifyInput {
 }
 
 const HISTORY_KEY = "subfeed.notifications";
+const SETTINGS_KEY = "subfeed.notifSettings";
 const MAX_HISTORY = 100;
-const DEFAULT_TTL = 6000;
 const ERROR_TTL = 15000;
 
+// 6b: per-account notification settings (persisted by the Settings panel into the
+// server `preferences`, mirrored to localStorage so they apply before login).
+export interface NotifSettings {
+  sound: boolean; // play a short tone on attention-needing notifications
+  durationMs: number; // auto-dismiss time for info/success toasts
+}
+const DEFAULT_SETTINGS: NotifSettings = { sound: false, durationMs: 6000 };
+let config: NotifSettings = loadSettings();
+
+function loadSettings(): NotifSettings {
+  try {
+    return { ...DEFAULT_SETTINGS, ...JSON.parse(localStorage.getItem(SETTINGS_KEY) || "{}") };
+  } catch {
+    return DEFAULT_SETTINGS;
+  }
+}
+
+export function getNotifSettings(): NotifSettings {
+  return config;
+}
+
+export function configureNotifications(p: Partial<NotifSettings>): void {
+  config = { ...config, ...p };
+  try {
+    localStorage.setItem(SETTINGS_KEY, JSON.stringify(config));
+  } catch {
+    /* ignore */
+  }
+}
+
+let audioCtx: AudioContext | null = null;
+function beep(): void {
+  try {
+    const Ctx = window.AudioContext || (window as unknown as { webkitAudioContext: typeof AudioContext }).webkitAudioContext;
+    audioCtx = audioCtx || new Ctx();
+    const osc = audioCtx.createOscillator();
+    const gain = audioCtx.createGain();
+    osc.connect(gain);
+    gain.connect(audioCtx.destination);
+    osc.frequency.value = 660;
+    gain.gain.value = 0.04;
+    osc.start();
+    osc.stop(audioCtx.currentTime + 0.12);
+  } catch {
+    /* autoplay blocked or unsupported — ignore */
+  }
+}
+
 let items: Notification[] = load();
 let listeners: Array<() => void> = [];
 let counter = items.reduce((m, n) => Math.max(m, n.id), 0) + 1;
@@ -107,7 +155,7 @@ export function notify(input: NotifyInput): number {
     ? undefined
     : level === "error" || level === "fatal"
       ? ERROR_TTL
-      : DEFAULT_TTL;
+      : config.durationMs;
   items = [
     ...items,
     {
@@ -125,6 +173,9 @@ export function notify(input: NotifyInput): number {
     },
   ];
   emit();
+  if (config.sound && (requiresInteraction || level === "error" || level === "fatal")) {
+    beep();
+  }
   if (duration) setTimeout(() => dismiss(id), duration);
   return id;
 }