Fix: Don't show fallback servers when not logged in

Blossom uploads require signed auth events, so users must be logged in.
The 'Account required' message is already shown in this case.

src/components/BlossomUploadDialog.tsx

@@ -124,9 +124,9 @@ export function BlossomUploadDialog({
       return;
     }
 
-    // If no pubkey (not logged in), use fallback servers
+    // If no pubkey (not logged in), can't upload - auth required
     if (!pubkey) {
-      useFallbackServers();
+      setLoadingServers(false);
       return;
     }