Serve community products from local packs

The proxy serves products from local packs (t5de-api's format) under local IDs from 2,000,000,000: product
info and permission answers (with the parent's derivation chain from IMVU), the product's CFL, and the shop's
bundle lookup. Community products are taken out of outfit saves and outfit chat commands before IMVU sees
them, remembered per account with the outfit they belong to, and added back when the client loads that
outfit. Changed requests are re-signed with the session key from the login response.

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

internal/products/chat.go

@@ -22,6 +22,7 @@ type strippedCommand struct {
 	empty    bool    // nothing is left to send
 	outfit   bool    // the line was a whole outfit (*use with the body)
 	products []int64 // the community products it named
+	kept     []int64 // the other products it named
 }
 
 // stripCommand takes products for which isCommunity is true out of an outfit command's arguments.
@@ -41,6 +42,9 @@ func stripCommand(text string, isCommunity func(int64) bool) strippedCommand {
 			r.products = append(r.products, id)
 			continue
 		}
+		if err == nil {
+			r.kept = append(r.kept, id)
+		}
 		kept = append(kept, f)
 	}
 	if len(r.products) == 0 {