fix(demo): nostr-rs-relay icon (nostr.svg missing → nostrudel.svg)

The catalog pointed at a non-existent nostr.svg (handleImageError only falls
back .png→.svg, so an .svg miss stays broken). Point it at the existing nostr
icon. fedimint icon already uses fedimint.png (exists); the stale fedimint.jpg
request is resolved by /api/app-catalog now serving the local catalog.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app-catalog/catalog.json

@@ -195,7 +195,7 @@
       "title": "Nostr Relay (Rust)",
       "version": "0.8.0",
       "description": "High-performance Nostr relay written in Rust. Host your own decentralized social media relay and earn networking profits.",
-      "icon": "/assets/img/app-icons/nostr.svg",
+      "icon": "/assets/img/app-icons/nostrudel.svg",
       "author": "Nostr RS Relay",
       "category": "community",
       "tier": "recommended",

neode-ui/public/catalog.json

@@ -195,7 +195,7 @@
       "title": "Nostr Relay (Rust)",
       "version": "0.8.0",
       "description": "High-performance Nostr relay written in Rust. Host your own decentralized social media relay and earn networking profits.",
-      "icon": "/assets/img/app-icons/nostr.svg",
+      "icon": "/assets/img/app-icons/nostrudel.svg",
       "author": "Nostr RS Relay",
       "category": "community",
       "tier": "recommended",