web-ui: raise proxy body limit to 100mb for large document uploads

Default 10mb caused upload-tagged 500s on scanned PDFs in case 1027-26
(Next 16 truncates body, FastAPI sees broken multipart, socket hang up).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web-ui/next.config.ts

@@ -13,6 +13,10 @@ const API_ORIGIN =
 const nextConfig: NextConfig = {
   output: "standalone",
 
+  experimental: {
+    proxyClientMaxBodySize: "100mb",
+  },
+
   async rewrites() {
     return [
       {