fix(modals): drop double-card chrome from inner editor div

The outer <dialog id="modal-container" class="modal modal-wide"> already
provides border, background, max-width, and padding. After Task 8.5
broadened the CSS to also match div.modal, the inner div was painting
its own card chrome inside the outer one — card-in-a-card visual.

Strip class="modal modal-wide" and role="document" from the inner div.
Standalone-mode renders the editor as flat content under <main> (the
"this URL is also a real page" promise; full-page = full-page, not a
modal-over-nothing).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

l4d2web/l4d2web/templates/overlay_file_editor.html

@@ -2,7 +2,7 @@
 {% block title %}Edit {{ rel_path }} · {{ overlay.name }}{% endblock %}
 {% block extra_head %}{% include "_editor_assets.html" %}{% endblock %}
 {% block content %}
-<div id="files-editor-modal" class="modal modal-wide" role="document" aria-labelledby="files-editor-title">
+<div id="files-editor-modal" aria-labelledby="files-editor-title">
   <div class="modal-header">
     <h2 id="files-editor-title" class="files-editor-path">
       <span class="files-editor-title-text">{{ rel_path }}</span>