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/lib/nostr/client.ts

@@ -0,0 +1,44 @@
+import { SimplePool, getPublicKey, nip19 } from 'nostr-tools'
+
+export interface NostrClientConfig {
+  relays: string[]
+}
+
+export class NostrClient {
+  private pool: SimplePool
+  private relays: string[]
+  private _isConnected: boolean = false
+
+  constructor(config: NostrClientConfig) {
+    this.pool = new SimplePool()
+    this.relays = config.relays
+  }
+
+  get isConnected(): boolean {
+    return this._isConnected
+  }
+
+  async connect(): Promise<void> {
+    try {
+      // Try to connect to at least one relay
+      const connections = await Promise.allSettled(
+        this.relays.map(relay => this.pool.ensureRelay(relay))
+      )
+
+      // Check if at least one connection was successful
+      this._isConnected = connections.some(result => result.status === 'fulfilled')
+
+      if (!this._isConnected) {
+        throw new Error('Failed to connect to any relay')
+      }
+    } catch (error) {
+      this._isConnected = false
+      throw error
+    }
+  }
+
+  disconnect(): void {
+    this.pool.close(this.relays)
+    this._isConnected = false
+  }
+}