Refresh the inventory on the user's queue, which the client joins by connecting

The client never subscribes to its user queue; the proxy now follows every IMQ connection and the signed-in
account (from the login answer), and delivers the refresh event on /user/<id>. Checked live: removing a product
from the library on the hub reloads the client's inventory.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

internal/products/products.go

@@ -60,6 +60,8 @@ type Products struct {
 
 	roomMu sync.Mutex
 	room   room
+
+	user string // the signed-in IMVU account (from the login answer), under mu
 }
 
 // Ready is told a product arrived (the fetcher wrote it): it's served from now on, and given to the client for