feat(phase6): video grid, noise suppression, whisper system

- New VideoGrid component: live camera feeds (local + remote) in VoicePanel
- Camera toggle in VoiceControls: enable/disable video per participant
- Noise suppression toggle in VoiceControls + voice store
- VOICE_WHISPER WS event: backend routes whisper to target user only
- Whisper UI: per-participant whisper button, notification toasts with dismiss
- Fix circular import between voice.ts and ws.ts (use lazy accessor)

internal/gateway/client.go

@@ -142,6 +142,23 @@ func (c *Client) readPump() {
 		switch event.Type {
 		case EventTypingStart, EventPresenceUpdate:
 			c.Hub.BroadcastEvent(event)
+		case EventVoiceWhisper:
+			// Forward voice whispers only to the target user, not broadcast
+			var whisperData struct {
+				TargetUserID string `json:"target_user_id"`
+				FromUserID   string `json:"from_user_id"`
+				FromUsername string `json:"from_username"`
+				Message      string `json:"message,omitempty"`
+			}
+			if raw, ok := event.Data.(json.RawMessage); ok {
+				if err := json.Unmarshal(raw, &whisperData); err == nil {
+					whisperData.FromUserID = c.UserID
+					c.Hub.SendToUser(whisperData.TargetUserID, Event{
+						Type: EventVoiceWhisper,
+						Data: whisperData,
+					})
+				}
+			}
 		default:
 			c.Hub.logger.Info("received event from client", "type", event.Type, "user_id", c.UserID)
 		}

internal/gateway/events.go

@@ -22,6 +22,7 @@ const (
 	EventVoiceLeave     = "VOICE_LEAVE"
 	EventVoiceMute      = "VOICE_MUTE"
 	EventVoiceDeafen    = "VOICE_DEAFEN"
+	EventVoiceWhisper   = "VOICE_WHISPER"
 )
 
 // Event represents a WebSocket event sent to clients.

internal/gateway/hub.go

@@ -227,6 +227,28 @@ func (h *Hub) ClientCount() int {
 	return len(h.clients)
 }
 
+// SendToUser sends an event only to the specified user's connected client(s).
+func (h *Hub) SendToUser(userID string, event Event) {
+	data, err := json.Marshal(event)
+	if err != nil {
+		h.logger.Error("failed to marshal event", "type", event.Type, "error", err)
+		return
+	}
+
+	h.mu.RLock()
+	defer h.mu.RUnlock()
+
+	for client := range h.clients {
+		if client.UserID == userID {
+			select {
+			case client.send <- data:
+			default:
+				go func(c *Client) { h.unregister <- c }(client)
+			}
+		}
+	}
+}
+
 // RefreshUserServers loads the server membership for a user from the database
 // and caches it. Call when a client connects or when server membership changes.
 func (h *Hub) RefreshUserServers(userID string) {