feat(nostr): Implement Nostr Feed with real-time note fetching

- Add NostrFeed component to display Nostr network notes
- Integrate date-fns for human-readable timestamp formatting
- Enhance NostrClient with fetchNotes and subscribeToNotes methods
- Implement loading, error, and empty state handling
- Add scrollable card-based UI for note display
- Configure dynamic relay selection with fallback to environment variables

package.json

@@ -15,6 +15,7 @@
     "@vueuse/head": "^2.0.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "date-fns": "^4.1.0",
     "fuse.js": "^7.0.0",
     "lucide-vue-next": "^0.474.0",
     "nostr-tools": "^2.10.4",