feat: knock notifications for admins + AFK auto-mute in calls

P4-3 — Knock-to-join Notifications for Admins:
- usePendingKnocks() hook reactively tracks knocking members via
  RoomMemberEvent.Membership; returns empty array if user lacks invite power
- Members icon in RoomViewHeader shows a Warning badge with the knock count
  when there are pending requests; badge updates in real time without
  needing to open the drawer; aria-label updated to describe pending count

P5-11 — AFK Auto-Mute in Voice:
- useAfkAutoMute() hook opens a monitoring-only getUserMedia stream,
  connects it to an AnalyserNode, and polls RMS every 500ms
- If mic is on and RMS stays below threshold for the configured timeout,
  calls callEmbed.control.setMicrophone(false) and shows an in-app toast
- Hook is called inside CallControls so monitoring is only active during calls
- Settings: afkAutoMute toggle + afkTimeoutMinutes select (1/5/10/20/30 min,
  default 10) added to Settings → Calls

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/state/settings.ts

@@ -128,6 +128,9 @@ export interface Settings {
 
   mentionHighlightColor: string;
   fontFamily: 'system' | 'inter' | 'jetbrains-mono' | 'fira-code';
+
+  afkAutoMute: boolean;
+  afkTimeoutMinutes: number;
 }
 
 const defaultSettings: Settings = {
@@ -198,6 +201,9 @@ const defaultSettings: Settings = {
 
   mentionHighlightColor: '',
   fontFamily: 'inter',
+
+  afkAutoMute: false,
+  afkTimeoutMinutes: 10,
 };
 
 export const getSettings = (): Settings => {