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/features/settings/general/General.tsx

@@ -1111,6 +1111,8 @@ function Calls() {
   const [pttMode, setPttMode] = useSetting(settingsAtom, 'pttMode');
   const [pttKey, setPttKey] = useSetting(settingsAtom, 'pttKey');
   const [deafenKey, setDeafenKey] = useSetting(settingsAtom, 'deafenKey');
+  const [afkAutoMute, setAfkAutoMute] = useSetting(settingsAtom, 'afkAutoMute');
+  const [afkTimeoutMinutes, setAfkTimeoutMinutes] = useSetting(settingsAtom, 'afkTimeoutMinutes');
 
   const pttBind = useKeyBind(setPttKey);
   const deafenBind = useKeyBind(setDeafenKey);
@@ -1186,6 +1188,45 @@ function Calls() {
           }
         />
       </SequenceCard>
+      <SequenceCard
+        className={SequenceCardStyle}
+        variant="SurfaceVariant"
+        direction="Column"
+        gap="400"
+      >
+        <SettingTile
+          title="AFK Auto-Mute"
+          description="Automatically mute your microphone when you have been silent in a call."
+          after={<Switch variant="Primary" value={afkAutoMute} onChange={setAfkAutoMute} />}
+        />
+        {afkAutoMute && (
+          <SettingTile
+            title="Idle Timeout"
+            description="How long to wait before auto-muting."
+            after={
+              <select
+                value={afkTimeoutMinutes}
+                onChange={(e) => setAfkTimeoutMinutes(Number(e.target.value))}
+                style={{
+                  background: 'var(--bg-surface)',
+                  color: 'inherit',
+                  border: '1px solid var(--border-interactive-normal)',
+                  borderRadius: '6px',
+                  padding: '4px 8px',
+                  fontSize: 'inherit',
+                  cursor: 'pointer',
+                }}
+              >
+                <option value={1}>1 minute</option>
+                <option value={5}>5 minutes</option>
+                <option value={10}>10 minutes</option>
+                <option value={20}>20 minutes</option>
+                <option value={30}>30 minutes</option>
+              </select>
+            }
+          />
+        )}
+      </SequenceCard>
     </Box>
   );
 }