Fix asset manifest using link_tree for controllers

- Use link_tree for controllers directory instead of individual files
- Update index.js to import application from controllers/application
- Follows Rails engine best practices for asset organization
- Simpler and more maintainable approach

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

Co-Authored-By: Claude <[email protected]>

Author: kieranklaassen

app/assets/config/leva_manifest.js

@@ -1,4 +1,4 @@
 //= link_directory ../stylesheets/leva .css
 //= link_directory ../builds/leva .css
-//= link_tree ../../javascript .js
+//= link_tree ../../javascript/controllers .js
 //= link_tree ../../../vendor/javascript .js

app/javascript/controllers/index.js

@@ -1,6 +1,6 @@
 // Import and register all your controllers from the importmap
 
-import { application } from "application"
+import { application } from "controllers/application"
 
 // Eager load all controllers defined in the import map under controllers/**/*_controller
 import { eagerLoadControllersFrom } from "@hotwired/stimulus-loading"