Fix grid column misalignment caused by hidden expand button

display:none removes element from grid flow, shifting other columns.
Use visibility:hidden instead so the expand button always holds its cell.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/app.mjs

@@ -346,10 +346,10 @@ function make_entry_row(entry, children_map) {
 	row.dataset.priority = entry.priority;
 	row.dataset.status   = entry.status;
 
-	// Expand button — hidden in flat mode
+	// Expand button — invisible in flat mode or when no children
 	const expand_btn = row.querySelector('.btn-expand');
 	if (!state.flat_mode && children.length > 0) {
-		show(expand_btn);
+		expand_btn.style.visibility = 'visible';
 		expand_btn.textContent = state.expanded.has(entry.id) ? '▼' : '▶';
 		expand_btn.addEventListener('click', () => {
 			if (state.expanded.has(entry.id)) { state.expanded.delete(entry.id); }

public/style.css

@@ -198,6 +198,7 @@ main { padding: 1.25rem; }
 	display: flex;
 	align-items: center;
 	justify-content: center;
+	visibility: hidden;
 }
 .btn-expand:hover { color: #aaa; background: #333; }
 

public/templates.html

@@ -1,7 +1,7 @@
 <!-- Entry list item -->
 <template id="t-entry-row">
 	<div class="task-row">
-		<button class="btn-expand" hidden></button>
+		<button class="btn-expand"></button>
 		<div class="task-meta">
 			<div class="entry-type-chip" hidden></div>
 			<span class="task-id"></span>