fix: read-only rich text — use plain div instead of admin-form-input

admin-form-input has fixed height (36px) causing overflow. Replaced
with a styled div matching the editor appearance. No new CSS needed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/admin/admin.css

@@ -383,27 +383,6 @@ img {
   max-width: 100%;
 }
 
-/* Rich text content rendered as read-only inside form inputs */
-.admin-form-input.section-content {
-  height: auto;
-  white-space: normal;
-  word-break: break-word;
-}
-
-.admin-form-input.section-content ul,
-.admin-form-input.section-content ol {
-  margin: 0 0 0.4em 1.5em;
-  padding: 0;
-}
-
-.admin-form-input.section-content li {
-  margin-bottom: 0.2em;
-}
-
-.admin-form-input.section-content p {
-  margin: 0 0 0.4em 0;
-}
-
 .admin-form-input[type="number"]::-webkit-inner-spin-button,
 .admin-form-input[type="number"]::-webkit-outer-spin-button {
   -webkit-appearance: none;