Scope htmx history to .main-container so menu survives Back

Previously, htmx cached the entire HTML body for browser back-and-forth
navigation. On a history-cache miss (for example, after a historyCacheError
caused by exceeding the localStorage quota), it re-fetches the page.
However, for htmx requests, this re-fetch omits the top menu, effectively
wiping it.

Mark .main-container with hx-history-elt so htmx caches and restores only
the content area. This also reduces the localStorage quota pressure.

Since historyElt is limited to .main-container, it no longer contains
.ck-body-wrapper. The cleanup is redundant anyway, as fa61ab1 fixed the
underlying CKEditor teardown.

Author: sunnavy

share/html/Elements/Header

@@ -119,14 +119,15 @@
       hx-target="this"
       hx-select=".main-container"
       hx-swap="outerHTML"
+      hx-history-elt
       <% $id && qq[id="comp-$id"] |n %>
     >
       <& /Widgets/Spinner &>
       <div id='rt-header-container'>
       <& Footer &>
 % $m->abort;
 % } else {
-    <div class="<% join( ' ', @{$ARGS{'MainContainerClass'}} ) %>" <% $id && qq[id="comp-$id"] |n %>>
+    <div class="<% join( ' ', @{$ARGS{'MainContainerClass'}} ) %>" hx-history-elt <% $id && qq[id="comp-$id"] |n %>>
 
 %# To refresh main container, here we create a separated div so its hx-* attributes are not inherited.
       <div

share/static/js/init.js

@@ -76,11 +76,11 @@ document.addEventListener('htmx:beforeHistorySave', function(evt) {
     }
 
     evt.detail.historyElt.querySelector('#hx-boost-spinner').classList.add('invisible');
-    evt.detail.historyElt.querySelector('.main-container').classList.remove('refreshing');
+    // historyElt is the .main-container itself, so clear .refreshing on it directly.
+    evt.detail.historyElt.classList.remove('refreshing');
     evt.detail.historyElt.querySelectorAll('textarea.richtext').forEach(function(elt) {
         RT.CKEditor.instances[elt.name]?.destroy();
     });
-    evt.detail.historyElt.querySelector('.ck-body-wrapper')?.remove();
 
     evt.detail.historyElt.querySelectorAll('.tomselected').forEach(elt => elt.tomselect?.destroy());
     evt.detail.historyElt.querySelectorAll('.dropzone-init').forEach(elt => elt.dropzone?.destroy());