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

Dockerfile.frontend

@@ -0,0 +1,40 @@
+# ============================================================================
+# DAARION Frontend Dockerfile
+# Multi-stage build for production
+# ============================================================================
+
+# Stage 1: Build
+FROM node:18-alpine AS builder
+
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm ci --only=production
+
+# Copy source
+COPY . .
+
+# Build frontend
+RUN npm run build
+
+# Stage 2: Production
+FROM nginx:alpine
+
+# Copy built files
+COPY --from=builder /app/dist /usr/share/nginx/html
+
+# Copy nginx config for SPA
+COPY nginx/frontend.conf /etc/nginx/conf.d/default.conf
+
+# Expose port
+EXPOSE 80
+
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=5s --retries=3 \
+    CMD wget --spider -q http://localhost/health || exit 1
+
+CMD ["nginx", "-g", "daemon off;"]
+