docs(config): annotate multipart limits explaining JSON body is not covered

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

backend/src/main/resources/application.yml

@@ -21,6 +21,10 @@ spring:
 
   servlet:
     multipart:
+      # NOTE: these limits only apply to multipart/form-data uploads.
+      # Images sent as base64 inside a JSON body (Content-Type: application/json)
+      # are NOT constrained here — the @Size(max=7_000_000) annotation on
+      # RecipeCreateRequest.heroImageUrl enforces the limit for that path.
       max-file-size: 5MB
       max-request-size: 6MB