Shell: grouped, collapsible, multi-column per-tile settings popover

The gear popover learns the admin form's conventions: an instanceSchema
field's `group` starts a labeled subsection, `help` puts a line of guidance
under a control, and a manifest `instanceGroups[name]` adds
{ collapsed, columns, help } for that group (rendered as <details> with a
grid body; container queries drop to two or one column in narrow tiles).
/api/modules now exposes instanceGroups. Lets a module keep a long
show/hide checklist per tile — where display choices belong — without
the popover turning into a scroll of thirty loose checkboxes.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/shell.js

@@ -934,11 +934,54 @@ function toggleSettingsPopover(tile, el) {
   pop.className = 'tile-settings';
   const inputs = new Map();
 
+  // Fields render in schema order; a field's `group` starts a labeled
+  // subsection that consecutive same-group fields share, and the manifest's
+  // optional `instanceGroups[name]` adds { collapsed, columns, help } —
+  // the same conventions as the admin page's config form.
+  const groupMeta = man.instanceGroups && typeof man.instanceGroups === 'object' ? man.instanceGroups : {};
+  let groupName = null;
+  let container = pop;
+
   for (const [key, spec] of Object.entries(man.instanceSchema)) {
     const type = spec?.type || 'string';
     const label = spec?.label || key;
     const current = key in (tile.settings || {}) ? tile.settings[key] : spec?.default;
 
+    const g = spec?.group || '';
+    if (g !== groupName) {
+      groupName = g;
+      if (g) {
+        const meta = groupMeta[g] && typeof groupMeta[g] === 'object' ? groupMeta[g] : {};
+        const folds = meta.collapsed !== undefined;
+        const group = document.createElement(folds ? 'details' : 'div');
+        group.className = 'field-group';
+        if (folds) group.open = !meta.collapsed;
+        const title = document.createElement(folds ? 'summary' : 'div');
+        title.className = 'field-group-title';
+        title.textContent = g;
+        group.appendChild(title);
+        const body = document.createElement('div');
+        body.className = 'field-group-body';
+        const cols = Math.min(4, Math.trunc(Number(meta.columns)) || 0);
+        if (cols > 1) {
+          body.classList.add('is-columns');
+          body.style.setProperty('--cols', String(cols));
+        }
+        if (meta.help) {
+          const help = document.createElement('div');
+          help.className = 'field-group-help';
+          help.textContent = meta.help;
+          body.appendChild(help);
+        }
+        group.appendChild(body);
+        pop.appendChild(group);
+        pop.classList.add('has-groups');
+        container = body;
+      } else {
+        container = pop;
+      }
+    }
+
     const field = document.createElement('label');
     field.className = 'field' + (type === 'boolean' ? ' check' : '');
 
@@ -970,7 +1013,13 @@ function toggleSettingsPopover(tile, el) {
       field.append(span, input);
       inputs.set(key, () => (type === 'number' ? Number(input.value) : input.value));
     }
-    pop.appendChild(field);
+    if (spec?.help) {
+      const help = document.createElement('small');
+      help.className = 'field-help';
+      help.textContent = spec.help;
+      field.appendChild(help);
+    }
+    container.appendChild(field);
   }
 
   const actions = document.createElement('div');