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

scripts/stop-phase8.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+# ============================================================================
+# Stop Phase 8 — DAO Dashboard
+# ============================================================================
+
+echo "🛑 Stopping DAARION Phase 8 services..."
+docker-compose -f docker-compose.phase8.yml down
+
+echo "✅ Phase 8 services stopped"
+