修复：补充 Docker COS 凭证配置，修复截图代理 404 问题

- docker-compose.yml 添加 COS_SECRET_ID/KEY/REGION/BUCKET 环境变量透传
- docker/.env 填入腾讯云 COS 凭证和截图回调地址
- AiRoiController 移除多余 @GetMapping 注解，消除 Spring 双注解警告

根因：容器未传入 COS 凭证 → CosUtil 初始化跳过 → proxyScreenshotImage 返回 null → 404

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

src/main/java/com/genersoft/iot/vmp/aiot/controller/AiRoiController.java

@@ -117,7 +117,6 @@ public class AiRoiController {
     }
 
     @Operation(summary = "截图图片代理（服务端从 COS 下载后返回）")
-    @GetMapping("/snap/image")
     @RequestMapping(value = "/snap/image", method = {RequestMethod.GET, RequestMethod.HEAD})
     public ResponseEntity<?> getSnapImage(@RequestParam String cameraCode, HttpServletRequest request) {
         // HEAD 请求：只检查是否存在，不返回图片数据