fix(frontend): Add client_max_body_size to fix 413 error on file upload

Problem: PKB document upload fails with HTTP 413 in SAE environment

Root cause: Nginx default client_max_body_size is only 1MB

Solution: Add client_max_body_size 50M in http block and location /api/ block

frontend-v2/nginx.conf

@@ -17,6 +17,9 @@ http {
     include       /etc/nginx/mime.types;
     default_type  application/octet-stream;
 
+    # ⚠️ 文件上传大小限制（默认只有 1MB，太小会导致 413 错误）
+    client_max_body_size 50M;  # 允许上传最大 50MB 文件
+
     # 日志格式
     log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                       '$status $body_bytes_sent "$http_referer" '
@@ -101,6 +104,9 @@ http {
 
         # 后端 API 代理（关键配置）
         location /api/ {
+            # 文件上传大小限制（PKB 文档上传等场景）
+            client_max_body_size 50M;
+            
             # 代理到后端服务
             proxy_pass http://backend;