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/ids_test.go

@@ -0,0 +1,16 @@
+package products
+
+import "testing"
+
+func TestParseID(t *testing.T) {
+	for s, want := range map[string]int64{"2000000008": 2000000008, "2000000008.0": 2000000008, " 80 ": 80, "2e9": 2000000000} {
+		if got, ok := parseID(s); !ok || got != want {
+			t.Errorf("parseID(%q) = %d, %v", s, got, ok)
+		}
+	}
+	for _, s := range []string{"", "1.5", "abc", "1e300"} {
+		if _, ok := parseID(s); ok {
+			t.Errorf("parseID(%q) ok", s)
+		}
+	}
+}