0.5.1

Fix screen share renegotiation, add deafen and server-wide voice state

- Fix screen share not working mid-call by triggering SDP renegotiation after addTrack/removeTrack
- Fix speaking indicators broadcast to target voice channel participants instead of text channel subscribers
- Track muted/deafened/streaming per-user in hub voice state and broadcast globally so all clients see status
- Add deafen toggle that mutes incoming audio and auto-mutes outgoing, with headphone icon in UI