feat: 集成 DeepSeek AI 服务

- 新增 backend 服务 (Express + TypeScript)
- 前端表单提交改为调用后端 API
- DeepSeek 增强分析结果，本地规则作为 fallback
- Docker 双容器部署：web (Nginx) + backend
- Nginx 反向代理 /api 到后端服务
- 本地开发支持 Vite 代理 + backend:dev 脚本

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -1,5 +1,3 @@
-version: '3.8'
-
 services:
   web:
     build:
@@ -9,6 +7,8 @@ services:
     ports:
       - "8801:80"
     restart: unless-stopped
+    depends_on:
+      - backend
     healthcheck:
       test: ["CMD", "wget", "-q", "--spider", "http://localhost/"]
       interval: 30s
@@ -18,6 +18,29 @@ services:
     networks:
       - tianxuan-network
 
+  backend:
+    build:
+      context: .
+      dockerfile: backend/Dockerfile
+    container_name: tianxuan-company-backend
+    restart: unless-stopped
+    env_file:
+      - .env
+    environment:
+      PORT: 3000
+      DEEPSEEK_API_KEY: ${DEEPSEEK_API_KEY}
+      DEEPSEEK_BASE_URL: ${DEEPSEEK_BASE_URL:-https://api.deepseek.com}
+      DEEPSEEK_MODEL: ${DEEPSEEK_MODEL:-deepseek-chat}
+      REQUEST_TIMEOUT_MS: ${REQUEST_TIMEOUT_MS:-20000}
+    healthcheck:
+      test: ["CMD", "node", "-e", "fetch('http://localhost:3000/api/health').then((res) => { if (!res.ok) process.exit(1); }).catch(() => process.exit(1))"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 10s
+    networks:
+      - tianxuan-network
+
 networks:
   tianxuan-network:
     driver: bridge