feat(frontend): increase file upload size limit to 256MB (#11634)

- Updated Next.js configuration to set body size limits for server
actions and API routes.
- Enhanced error handling in the API client to provide user-friendly
messages for file size errors.
- Added user-friendly error messages for 413 Payload Too Large responses
in API error parsing.

These changes ensure that file uploads are consistent with backend
limits and improve user experience during uploads.

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  <!-- Put your test plan here: -->
  - [x] Upload a file bigger than 10MB and it works
- [X] Upload a file bigger than 256MB and you see a official error
stating the max file size is 256MB

autogpt_platform/frontend/src/app/api/proxy/[...path]/route.ts

@@ -6,6 +6,10 @@ import {
 import { environment } from "@/services/environment";
 import { NextRequest, NextResponse } from "next/server";
 
+// Increase body size limit to 256MB to match backend file upload limit
+export const maxDuration = 300; // 5 minutes timeout for large uploads
+export const dynamic = "force-dynamic";
+
 function buildBackendUrl(path: string[], queryString: string): string {
   const backendPath = path.join("/");
   return `${environment.getAGPTServerBaseUrl()}/${backendPath}${queryString}`;