feat: Add presence heartbeat for Matrix online status

- matrix-gateway: POST /internal/matrix/presence/online endpoint
- usePresenceHeartbeat hook with activity tracking
- Auto away after 5 min inactivity
- Offline on page close/visibility change
- Integrated in MatrixChatRoom component

backend/services/wallet/wallet.adapter.ts

@@ -0,0 +1,36 @@
+/**
+ * Wallet Adapter (MVP Stub)
+ * 
+ * On MVP: returns mock data or reads from DB/stub
+ * Future: integrate with on-chain data
+ */
+
+import type { Balance } from '../../domain/wallet/types';
+
+/**
+ * Get balances from external source (on-chain / DB / stub)
+ */
+export async function getBalances(userId: string): Promise<Balance[]> {
+  // MVP: Return mock data
+  // TODO: Replace with actual DB/on-chain integration
+  return [
+    { symbol: 'DAAR', amount: '0.0' },
+    { symbol: 'DAARION', amount: '0.0' },
+  ];
+}
+
+/**
+ * Get staked DAARION amount
+ */
+export async function getStakedDaarion(userId: string): Promise<number> {
+  // MVP: Return mock data
+  // TODO: Replace with actual DB/on-chain integration
+  return 0.0;
+}
+
+export const walletAdapter = {
+  getBalances,
+  getStakedDaarion,
+};
+
+