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/infra/db/dao.repository.ts

@@ -0,0 +1,44 @@
+/**
+ * DAO Repository
+ * Database access layer for DAO records
+ * MVP: In-memory storage, replace with actual DB later
+ */
+
+import type { DaoRecord } from '../../domain/dao/types';
+
+// MVP: In-memory storage
+const daoStore: Map<string, DaoRecord> = new Map();
+
+export const daoRepository = {
+  async save(record: DaoRecord): Promise<void> {
+    daoStore.set(record.daoId, record);
+  },
+
+  async findById(daoId: string): Promise<DaoRecord | null> {
+    return daoStore.get(daoId) || null;
+  },
+
+  async findAll(filter?: { level?: string; type?: string }): Promise<DaoRecord[]> {
+    const all = Array.from(daoStore.values());
+    
+    if (!filter) {
+      return all;
+    }
+
+    return all.filter(dao => {
+      if (filter.level && dao.level !== filter.level) {
+        return false;
+      }
+      if (filter.type && dao.type !== filter.type) {
+        return false;
+      }
+      return true;
+    });
+  },
+
+  async delete(daoId: string): Promise<void> {
+    daoStore.delete(daoId);
+  },
+};
+
+