Add redirect for GET requests to /upload endpoint

Added a redirect handler for users who try to access /upload via GET
request instead of using the form POST. This prevents errors and guides
users to the proper upload form.

Changes:
- Added GET route for /upload that redirects to benefit forms page
- Added redirect_to_benefit_forms action in controller
- Shows info flash message directing users to the upload form

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

config/routes.rb

@@ -34,6 +34,7 @@ Railsgoat::Application.routes.draw do
   end
 
   get "download" => "benefit_forms#download"
+  get "upload" => "benefit_forms#redirect_to_benefit_forms"
   post "upload" => "benefit_forms#upload"
 
   resources :tutorials do