Fix toggle_attribute disabled check for checkbox inputs

Use the computed `value` and `dataValue` variables instead of raw
`event.target.value` and `this.dataset.value` when setting the
disabled state on hidden inputs. For checkboxes, event.target.value
returns the HTML value attribute (e.g. "true") rather than the
checked state, causing the disabled toggle to always evaluate
incorrectly.

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

app/javascript/elements/toggle_attribute.js

@@ -14,7 +14,7 @@ export default class extends HTMLElement {
         this.target.classList.toggle(this.dataset.className, value !== dataValue)
 
         if (this.dataset.className === 'hidden' && this.target.tagName === 'INPUT') {
-          this.target.disabled = event.target.value !== this.dataset.value
+          this.target.disabled = value !== dataValue
         }
       }