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/stores/nostr.ts

@@ -1,5 +1,7 @@
 import { defineStore } from 'pinia'
 import { ref } from 'vue'
+import { NostrClient } from '@/lib/nostr/client'
+import { config } from '@/lib/config'
 
 // Define an interface for the account object
 interface NostrAccount {
@@ -8,16 +10,67 @@ interface NostrAccount {
 }
 
 export const useNostrStore = defineStore('nostr', () => {
+  // Connection state
   const isConnected = ref(false)
-  const relayUrls = ref<string[]>([])
+  const isConnecting = ref(false)
+  const error = ref<Error | null>(null)
+  
+  // Configuration
+  const relayUrls = ref<string[]>(config.nostr.relays)
   const account = ref<NostrAccount | null>(null)
+  
+  // Singleton client instance
+  let client: NostrClient | null = null
 
+  // Get or create client instance
+  function getClient(): NostrClient {
+    if (!client) {
+      client = new NostrClient({ relays: relayUrls.value })
+    }
+    return client
+  }
+
+  // Connection management
+  async function connect(): Promise<void> {
+    try {
+      error.value = null
+      isConnecting.value = true
+      
+      const nostrClient = getClient()
+      await nostrClient.connect()
+      
+      isConnected.value = nostrClient.isConnected
+    } catch (err) {
+      error.value = err instanceof Error ? err : new Error('Failed to connect')
+      isConnected.value = false
+      throw err
+    } finally {
+      isConnecting.value = false
+    }
+  }
+
+  function disconnect(): void {
+    if (client) {
+      client.disconnect()
+      client = null
+    }
+    isConnected.value = false
+    isConnecting.value = false
+    error.value = null
+  }
+
+  // Configuration setters
   function setConnected(value: boolean) {
     isConnected.value = value
   }
 
   function setRelayUrls(urls: string[]) {
     relayUrls.value = urls
+    // Recreate client with new relays
+    if (client) {
+      client.disconnect()
+      client = null
+    }
   }
 
   function setAccount(nostrAccount: NostrAccount | null) {
@@ -25,9 +78,17 @@ export const useNostrStore = defineStore('nostr', () => {
   }
 
   return {
+    // State
     isConnected,
+    isConnecting,
+    error,
     relayUrls,
     account,
+    
+    // Actions
+    connect,
+    disconnect,
+    getClient,
     setConnected,
     setRelayUrls,
     setAccount,