feat(nostr): Add Nostr relay connection and status management

- Integrate nostr-tools for Nostr relay connectivity
- Create NostrClient for managing relay connections
- Implement useNostr composable for reactive connection handling
- Add ConnectionStatus component to display relay connection state
- Configure environment variable for Nostr relay endpoints
- Update App.vue to manage Nostr connection lifecycle

src/App.vue

@@ -1,7 +1,20 @@
 <script setup lang="ts">
+import { onMounted, onUnmounted } from 'vue'
 import Navbar from '@/components/layout/Navbar.vue'
 import Footer from '@/components/layout/Footer.vue'
+import ConnectionStatus from '@/components/nostr/ConnectionStatus.vue'
+import { useNostr } from '@/composables/useNostr'
 
+const relays = JSON.parse(import.meta.env.VITE_NOSTR_RELAYS as string)
+const { isConnected, error, connect, disconnect } = useNostr({ relays })
+
+onMounted(async () => {
+  await connect()
+})
+
+onUnmounted(() => {
+  disconnect()
+})
 </script>
 
 <template>
@@ -10,8 +23,9 @@ import Footer from '@/components/layout/Footer.vue'
       style="padding-top: env(safe-area-inset-top); padding-bottom: env(safe-area-inset-bottom)">
       <header
         class="sticky top-0 z-50 w-full border-b bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60">
-        <nav class="container flex h-14 items-center">
+        <nav class="container flex h-14 items-center justify-between">
           <Navbar />
+          <ConnectionStatus :is-connected="isConnected" :error="error" />
         </nav>
       </header>