Fix: prevent mobile web remote desktop freeze on Safari app-switch

by forcing clean WS reconnect on foreground return;

add 30-second grace period on server to avoid cold-start on quick reconnects

server/go/web/ws_handlers.go

@@ -244,7 +244,7 @@ func (h *wsHub) handleDisconnect(c *wsClient, _ []byte) {
 	h.mu.Unlock()
 	c.queue([]byte(`{"cmd":"disconnect_result","ok":true}`))
 	if prev != "" && h.countWatchers(prev) == 0 {
-		h.devices.CloseScreen(prev)
+		h.deferredCloseScreen(prev)
 	}
 }
 
@@ -288,6 +288,11 @@ func (h *wsHub) handleConnect(c *wsClient, raw []byte) {
 			c.queueBinary(cache.Keyframe)
 		}
 		h.mu.Lock()
+		// Cancel any pending deferred close so the relay stays alive.
+		if t, ok := h.screenCloseTimers[in.ID]; ok {
+			t.Stop()
+			delete(h.screenCloseTimers, in.ID)
+		}
 		c.watching = in.ID
 		h.mu.Unlock()
 		return