Fix lightbox blocking clicks on page elements

The CSS change in 39575a0 added `display: flex` to the lightbox dialog
unconditionally, which overrode the browser's default `display: none`
for closed dialogs. This made the invisible lightbox overlay intercept
all clicks on the page.

Move flexbox properties to the `&[open]` selector so they only apply
when the dialog is actually open.

Also fix typo: `innerHtml` → `innerHTML` (capital H).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/javascript/controllers/lightbox_controller.js

@@ -30,7 +30,7 @@ export default class extends Controller {
 
   reset() {
     this.zoomedImageTarget.src = ""
-    this.captionTarget.innerHtml = " "
+    this.captionTarget.innerHTML = " "
     this.dispatch('closed')
   }