refactor: Simplify Nostr connection management and enhance store integration

- Refactor useNostr composable to utilize a centralized Pinia store for connection state and client management.
- Update NostrFeed and App components to leverage the new store-based approach for relay configuration and client instantiation.
- Remove direct relay URL handling from components, improving maintainability and consistency across the application.

src/components/nostr/NostrFeed.vue

@@ -18,8 +18,7 @@ const notes = ref<NostrNote[]>([])
 const isLoading = ref(true)
 const error = ref<Error | null>(null)
 
-const relayUrls = props.relays || config.nostr.relays
-const { disconnect } = useNostr({ relays: relayUrls })
+const { getClient } = useNostr(props.relays ? { relays: props.relays } : undefined)
 
 // Get admin/moderator pubkeys from centralized config
 const adminPubkeys = config.nostr.adminPubkeys
@@ -29,7 +28,7 @@ async function loadNotes() {
     isLoading.value = true
     error.value = null
     
-    const client = new NostrClient({ relays: relayUrls })
+    const client = getClient()
     await client.connect()
     
     // Configure fetch options based on feed type