fix: 修复Docker构建和路径解析问题

- 在Dockerfile中使用npm中国镜像加速依赖安装
- 修正后端健康检查端点路径
- 修复Docker环境中图片路径解析问题
- 修正前端API地址默认值

backend/Dockerfile

@@ -12,8 +12,9 @@ WORKDIR /app
 COPY package*.json ./
 COPY prisma ./prisma/
 
-# Install dependencies
-RUN npm ci
+# Install dependencies with Chinese mirror
+RUN npm config set registry https://registry.npmmirror.com && \
+    npm ci
 
 # ========================================
 # Stage 2: Builder