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)
 		}