[client] Remove lazy connection UI toggle (#6661)

Lazy connections are now opt-out and controlled centrally by NB_LAZY_CONN,
MDM policy (lazyConnection), and the management feature flag (#6617). The
per-device UI toggle no longer fits this model: after #6617 the daemon stopped
persisting the setting and dropped it from GetConfig, so the Wails toggle always
read back OFF and its writes did not survive a restart.

Remove the toggle and the orphaned runtime plumbing, matching what main did for
the Fyne UI:
- drop the toggle from SettingsNetwork and the lazy i18n keys
- drop LazyConnectionEnabled from the UI settings service and SetConfig request
- drop the runtime-apply block in server.SetConfig
- delete Engine.SetLazyConnEnabled and ConnMgr.SetLocalLazyConn

The proto fields and FullStatus status reporting are left intact.

client/server/server.go

@@ -421,16 +421,6 @@ func (s *Server) SetConfig(callerCtx context.Context, msg *proto.SetConfigReques
 		return nil, fmt.Errorf("failed to update profile config: %w", err)
 	}
 
-	// Apply the lazy connection toggle to the running engine so it takes
-	// effect without a down/up. s.mutex is already held.
-	if msg.LazyConnectionEnabled != nil && s.connectClient != nil {
-		if engine := s.connectClient.Engine(); engine != nil {
-			if err := engine.SetLazyConnEnabled(msg.GetLazyConnectionEnabled()); err != nil {
-				log.Errorf("failed to apply lazy connection change at runtime: %v", err)
-			}
-		}
-	}
-
 	return &proto.SetConfigResponse{}, nil
 }