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/hooks/useAfkAutoMute.ts

@@ -0,0 +1,83 @@
+import { useEffect } from 'react';
+import { useSetAtom } from 'jotai';
+import { CallEmbed } from '../plugins/call';
+import { useSetting } from '../state/hooks/settings';
+import { settingsAtom } from '../state/settings';
+import { toastQueueAtom } from '../state/toast';
+
+const SILENCE_RMS_THRESHOLD = 0.008;
+const CHECK_INTERVAL_MS = 500;
+
+/**
+ * Monitors microphone audio while in a call. If the mic stays active but
+ * silent for longer than the configured timeout, the mic is muted and a
+ * toast is shown. Cleans up its own AudioContext and stream on unmount.
+ */
+export function useAfkAutoMute(callEmbed: CallEmbed | undefined): void {
+  const [enabled] = useSetting(settingsAtom, 'afkAutoMute');
+  const [timeoutMinutes] = useSetting(settingsAtom, 'afkTimeoutMinutes');
+  const setToast = useSetAtom(toastQueueAtom);
+
+  useEffect(() => {
+    if (!callEmbed || !enabled) return;
+
+    let stream: MediaStream | undefined;
+    let audioCtx: AudioContext | undefined;
+    let intervalId: ReturnType<typeof setInterval> | undefined;
+    let silenceStart: number | null = null;
+    let active = true;
+    const timeoutMs = timeoutMinutes * 60 * 1000;
+
+    navigator.mediaDevices
+      .getUserMedia({ audio: true, video: false })
+      .then((s) => {
+        if (!active) {
+          s.getTracks().forEach((t) => t.stop());
+          return;
+        }
+        stream = s;
+        audioCtx = new AudioContext();
+        const source = audioCtx.createMediaStreamSource(stream);
+        const analyser = audioCtx.createAnalyser();
+        analyser.fftSize = 256;
+        source.connect(analyser);
+        const buffer = new Float32Array(analyser.fftSize);
+
+        intervalId = setInterval(() => {
+          if (!active) return;
+          analyser.getFloatTimeDomainData(buffer);
+          const rms = Math.sqrt(buffer.reduce((sum, v) => sum + v * v, 0) / buffer.length);
+
+          if (rms > SILENCE_RMS_THRESHOLD) {
+            // Audio detected — reset the silence timer
+            silenceStart = null;
+          } else if (callEmbed.control.microphone) {
+            // Mic is on but silent — start or advance the timer
+            if (silenceStart === null) silenceStart = Date.now();
+            else if (Date.now() - silenceStart >= timeoutMs) {
+              callEmbed.control.setMicrophone(false);
+              setToast({
+                id: `afk-mute-${Date.now()}`,
+                displayName: 'Lotus Chat',
+                body: 'Your microphone was muted after inactivity.',
+                roomName: 'Voice call',
+                roomId: callEmbed.roomId,
+              });
+              silenceStart = null;
+            }
+          } else {
+            // Mic is already muted — don't count silence
+            silenceStart = null;
+          }
+        }, CHECK_INTERVAL_MS);
+      })
+      .catch(() => undefined);
+
+    return () => {
+      active = false;
+      if (intervalId !== undefined) clearInterval(intervalId);
+      stream?.getTracks().forEach((t) => t.stop());
+      audioCtx?.close().catch(() => undefined);
+    };
+  }, [callEmbed, enabled, timeoutMinutes, setToast]);
+}