Show T5 products in the client's shop; keep float IDs and unknown paths off IMVU

The shop's T5 filter (maturity_rating "t5") is answered from the hub's products, fetched so they can be
shown and tried on; buying T5 products adds them to the hub library, and product.php details for
community products are answered here.

The client sends some product IDs as floats ("2000000008.0"): product.php passed the worn community
product to IMVU that way. Every ID is now read either way, and products.Guard refuses any request to
IMVU that still names a local ID given out. T5DE_PROXY_DUMP logs request and response bodies.

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

internal/products/products.go

@@ -11,6 +11,7 @@ package products
 
 import (
 	"bytes"
+	"context"
 	"crypto/md5"
 	"encoding/hex"
 	"errors"
@@ -58,10 +59,17 @@ type Products struct {
 	// library, for hub products).
 	OnHide func(id string)
 
+	// Shop, if set, searches the hub's products for the shop's T5 filter; Fetch gets one into the hub's products
+	// now; AddToLibrary adds one to the person's library (buying it in the shop).
+	Shop         func(ctx context.Context, query string) ([]hub.Product, error)
+	Fetch        func(ctx context.Context, id string) error
+	AddToLibrary func(ctx context.Context, id string) error
+
 	roomMu sync.Mutex
 	room   room
 
-	user string // the signed-in IMVU account (from the login answer), under mu
+	user     string                 // the signed-in IMVU account (from the login answer), under mu
+	shopSeen map[string]hub.Product // hub products as the shop last listed them, under mu
 }
 
 // Ready is told a product arrived (the fetcher wrote it): it's served from now on, and given to the client for