部署：添加部署配置（nginx、systemd、Dockerfile），并改进会话列表与头像显示

deploy/Dockerfile.frontend

@@ -0,0 +1,12 @@
+FROM node:20-alpine AS builder
+WORKDIR /app
+COPY frontend/package*.json ./
+RUN npm ci
+COPY frontend/ ./
+RUN npm run build --prefix frontend
+
+FROM nginx:stable-alpine
+COPY --from=builder /app/frontend/dist /usr/share/nginx/html
+COPY deploy/nginx/chat.conf /etc/nginx/conf.d/default.conf
+EXPOSE 8443
+CMD ["nginx", "-g", "daemon off;"]