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/composables/useNostr.ts

@@ -1,38 +1,24 @@
-import { ref } from 'vue'
-import { NostrClient, type NostrClientConfig } from '@/lib/nostr/client'
+import { storeToRefs } from 'pinia'
+import { useNostrStore } from '@/stores/nostr'
+import type { NostrClientConfig } from '@/lib/nostr/client'
 
-export function useNostr(config: NostrClientConfig) {
-  const client = new NostrClient(config)
-  const isConnected = ref(false)
-  const isConnecting = ref(false)
-  const error = ref<Error | null>(null)
-
-  async function connect() {
-    try {
-      error.value = null
-      isConnecting.value = true
-      await client.connect()
-      isConnected.value = client.isConnected
-    } catch (err) {
-      error.value = err instanceof Error ? err : new Error('Failed to connect')
-      isConnected.value = false
-    } finally {
-      isConnecting.value = false
-    }
+export function useNostr(config?: NostrClientConfig) {
+  const store = useNostrStore()
+  
+  // If custom relays are provided, update the store
+  if (config?.relays) {
+    store.setRelayUrls(config.relays)
   }
 
-  function disconnect() {
-    client.disconnect()
-    isConnected.value = false
-    isConnecting.value = false
-    error.value = null
-  }
+  // Return reactive refs from the store
+  const { isConnected, isConnecting, error } = storeToRefs(store)
 
   return {
     isConnected,
     isConnecting,
     error,
-    connect,
-    disconnect
+    connect: store.connect,
+    disconnect: store.disconnect,
+    getClient: store.getClient
   }
 }