Voice channel move: user disappears from list but audio still plays in original channel

Bug description

When a user is dragged (moved) from one voice channel to another by a moderator, the user disappears from the channel list in the UI but their audio is still heard by other participants in the original channel.

The moved user appears to be in the destination channel visually, but their voice stream is not properly transferred — it remains connected to the original channel's LiveKit room.

Steps to reproduce

1. User A joins voice channel 1
2. User B (with Move Members permission) drags User A to voice channel 2
3. User A disappears from channel 1's member list and appears in channel 2
4. Users in channel 1 can still hear User A speaking
5. User A's audio is not heard in channel 2

Expected behavior

User A should be fully moved to channel 2: audio transfers to the new channel and is no longer heard in the old one.

Actual behavior

• UI updates correctly (user moves in the list)
• Audio stream stays connected to the original channel
• Creates a "ghost audio" situation

Environment

• Fluxer Canary (web app and desktop)
• Hosted instance (api.fluxer.app)

Additional context

This is different from #500 and #1331 (which are about the API PATCH endpoint disconnecting users entirely) and #727 (Flatpak/AppImage disconnecting on move). This is a client-side desync where the UI updates but the audio connection doesn't follow.