fix(batch): move the selection bar into the title row

Selecting an entry inserted the batch bar as a block above the grid, pushing
every row down ~60px — the list jumped under the cursor mid-click. The bar
now renders inside .content-header, to the right of "All items", and the
header reserves its height (min-height) so appearing and disappearing shifts
nothing at all.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/app.js

@@ -3708,8 +3708,7 @@ function renderBatchBar() {
         on: { click: clearChecked },
     }, withIcon('i-x', 'Clear')));
 
-    const content = $('.content');
-    content.insertBefore(bar, $('#entryGrid'));
+    $('.content-header').appendChild(bar);
 }
 
 // ============================================================