fix: strip query params from asset URLs before filesystem lookup

Icon URLs stored with cache-busting query params (e.g. ?v=123) caused
existsSync to fail, preventing Discord attachment fallback and leaving
unresolvable localhost URLs as thumbnails.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/lib/rarity.ts

@@ -18,5 +18,11 @@ export function getRarityConfig(rarity: string): { color: number; emoji: string;
 }
 
 export function defaultName(path: string): string {
-  return path.split("/").pop() || "image.png";
+  return stripQuery(path).split("/").pop() || "image.png";
+}
+
+/** Strip query parameters from a URL/path (e.g. "foo.png?v=123" → "foo.png") */
+export function stripQuery(url: string): string {
+  const idx = url.indexOf("?");
+  return idx === -1 ? url : url.slice(0, idx);
 }