docs: clean upload documentation

lib/auth.ts

@@ -2,8 +2,7 @@ import { timingSafeEqual } from 'crypto'
 import { NextRequest, NextResponse } from 'next/server'
 
 /**
- * Validate the upload secret from request headers.
- * Returns null if valid, or a NextResponse error if invalid.
+ * Validate the shared upload secret before accepting mutation routes.
  */
 export function validateUploadSecret(req: NextRequest): NextResponse | null {
   const secret = req.headers.get('x-upload-secret')