fix(calls): sidebar voice-channel join respects the voice limit

channelFull was computed only in the prescreen; a second click on the
channel in the room nav joined a full channel. Extract
useVoiceChannelFull, use it in both places, and refuse with a
"Channel full (N/N)" toast.

Fixes #30

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/hooks/useVoiceChannelFull.ts

@@ -0,0 +1,34 @@
+import { Room } from 'matrix-js-sdk';
+import { useMemo } from 'react';
+import { useStateEvent } from './useStateEvent';
+import { StateEvent } from '../../types/matrix/room';
+import { VoiceLimitContent } from '../features/common-settings/general/RoomVoiceLimit';
+import { useCallMembers, useCallSession } from './useCall';
+import { useMatrixClient } from './useMatrixClient';
+
+export type VoiceChannelFull = {
+  channelFull: boolean;
+  current: number;
+  max: number;
+};
+
+/**
+ * [Gitea #30] Voice channel user limit (`io.lotus.voice_limit`), shared between
+ * `CallPrescreen` and any other join path (e.g. the room-nav second-click join)
+ * so they agree on when a channel is full. 0/absent `max_users` means no limit.
+ */
+export const useVoiceChannelFull = (room: Room): VoiceChannelFull => {
+  const mx = useMatrixClient();
+  const callSession = useCallSession(room);
+  const callMembers = useCallMembers(callSession);
+
+  const limitEvent = useStateEvent(room, StateEvent.LotusVoiceLimit);
+
+  return useMemo(() => {
+    const maxUsers = limitEvent?.getContent<VoiceLimitContent>().max_users ?? 0;
+    // A user already counted in the session is rejoining and should not be blocked.
+    const alreadyMember = callMembers.some((m) => m.sender === mx.getSafeUserId());
+    const channelFull = maxUsers > 0 && !alreadyMember && callMembers.length >= maxUsers;
+    return { channelFull, current: callMembers.length, max: maxUsers };
+  }, [limitEvent, callMembers, mx]);
+};