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/components/nostr/ConnectionStatus.vue

@@ -0,0 +1,20 @@
+<!-- A component that shows NOSTR connection status -->
+<script setup lang="ts">
+import { Badge } from '@/components/ui/badge'
+
+defineProps<{
+  isConnected: boolean
+  error?: Error | null
+}>()
+</script>
+
+<template>
+  <div class="flex items-center gap-2">
+    <Badge :variant="isConnected ? 'default' : 'destructive'" class="h-5">
+      NOSTR: {{ isConnected ? 'Connected' : 'Disconnected' }}
+    </Badge>
+    <p v-if="error" class="text-sm text-destructive">
+      {{ error.message }}
+    </p>
+  </div>
+</template>