tabs: extract scheduleField() helper — collapse 8 label/caption sites

Every field on the new- and edit-schedule forms (plus buildIntervalComposer
and buildTargetChips) builds the same wrapper shape:

    el('label', { class: 'schedule-field' },
      el('span', { class: 'schedule-field-label' }, '…'))

then appends an input. Eight identical-modulo-text sites. Extracting one
small helper:

    function scheduleField(labelText, ...children) {
      return el('label', { class: 'schedule-field' },
        el('span', { class: 'schedule-field-label' }, labelText),
        ...children);
    }

drops the per-site cost to a single `form_.append(scheduleField('caption',
input));` line. -10 LOC net; no behaviour change.

frontend/packages/dashboard/src/tabs.js

@@ -2004,6 +2004,18 @@ window.marked = marked;
     }
     return n;
   }
+  // Label + caption wrapper shared by every field on the schedule
+  // forms — `<label class="schedule-field"><span
+  // class="schedule-field-label">…</span>…children…</label>`. Variadic
+  // children land inside the label after the caption span, which is
+  // what every caller wants (the input + any preset/parts/preview
+  // sub-rows live next to the caption).
+  function scheduleField(labelText, ...children) {
+    return el('label', { class: 'schedule-field' },
+      el('span', { class: 'schedule-field-label' }, labelText),
+      ...children);
+  }
+
   // Interval composer (#466) — shared between the new-schedule form
   // and the edit-schedule form (#474). Builds the preset chip row +
   // d/h/m/s sub-fields + live preview, and returns helpers to read
@@ -2017,8 +2029,7 @@ window.marked = marked;
     namePrefix = 'interval_',
     initialSeconds = 0,
   } = {}) {
-    const wrapper = el('label', { class: 'schedule-field' },
+    const wrapper = scheduleField(label);
-      el('span', { class: 'schedule-field-label' }, label));
     const presets = [
       ['1m', 60], ['5m', 300], ['15m', 900], ['30m', 1800],
       ['1h', 3600], ['6h', 21600], ['12h', 43200],
@@ -2142,8 +2153,6 @@ window.marked = marked;
     // explicitly uncheckable. New-schedule callers pass `[]`.
     for (const n of extraNames) if (!candidates.includes(n)) candidates.push(n);
 
-    const label = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'targets'));
     const box = el('div', { class: 'schedule-targets' });
     for (const name of candidates) {
       const id_ = idPrefix + name;
@@ -2154,8 +2163,7 @@ window.marked = marked;
       box.append(el('label', { class: 'schedule-target-chip', for: id_ },
         cb, el('span', {}, name)));
     }
-    label.append(box);
+    return scheduleField('targets', box);
-    return label;
   }
 
   function renderScheduleNewForm() {
@@ -2181,17 +2189,12 @@ window.marked = marked;
       checked: new Set(carry.targets),
     }));
 
-    const bodyLabel = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'prompt body'));
     const bodyInput = el('textarea', {
       name: 'body', rows: '4', required: 'required', placeholder: 'message delivered to each target at fire time',
     });
     bodyInput.value = carry.body;
-    bodyLabel.append(bodyInput);
+    form_.append(scheduleField('prompt body', bodyInput));
-    form_.append(bodyLabel);
 
-    const firstFireLabel = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'first fire'));
     const firstFireInput = el('input', {
       type: 'datetime-local', name: 'first_fire', required: 'required',
     });
@@ -2200,8 +2203,7 @@ window.marked = marked;
     // immediately on a stale-clock accident).
     firstFireInput.value = carry.first_fire
       || isoForDatetimeLocal(new Date(Date.now() + 5 * 60 * 1000));
-    firstFireLabel.append(firstFireInput);
+    form_.append(scheduleField('first fire', firstFireInput));
-    form_.append(firstFireLabel);
 
     // Interval composer (#466). See `buildIntervalComposer` below —
     // shared between the new-schedule form and the edit-schedule form
@@ -2227,14 +2229,11 @@ window.marked = marked;
     }
     intervalCx.updatePreview();
 
-    const descLabel = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'description (optional)'));
     const descInput = el('input', {
       type: 'text', name: 'description', placeholder: 'shown on the schedule card',
     });
     descInput.value = carry.description;
-    descLabel.append(descInput);
+    form_.append(scheduleField('description (optional)', descInput));
-    form_.append(descLabel);
 
     const actions = el('div', { class: 'schedule-actions' });
     const submit = el('button', { type: 'submit', class: 'btn btn-spawn' }, '＋ qu3ue prompt');
@@ -2470,32 +2469,23 @@ window.marked = marked;
 
     const carry = scheduleEditCarry.get(s.id) || {};
 
-    const bodyLabel = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'body'));
     const bodyInput = el('textarea', { name: 'body', rows: '4', required: 'required' });
     bodyInput.value = carry.body !== undefined ? carry.body : s.body;
-    bodyLabel.append(bodyInput);
+    form_.append(scheduleField('body', bodyInput));
-    form_.append(bodyLabel);
 
-    const descLabel = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'description (blank to clear)'));
     const descInput = el('input', { type: 'text', name: 'description' });
     descInput.value = carry.description !== undefined
       ? carry.description
       : (s.description || '');
-    descLabel.append(descInput);
+    form_.append(scheduleField('description (blank to clear)', descInput));
-    form_.append(descLabel);
 
-    const firstFireLabel = el('label', { class: 'schedule-field' },
-      el('span', { class: 'schedule-field-label' }, 'next fire'));
     const firstFireInput = el('input', {
       type: 'datetime-local', name: 'next_fire', required: 'required',
     });
     firstFireInput.value = carry.next_fire !== undefined
       ? carry.next_fire
       : isoForDatetimeLocal(new Date(s.next_fire_at_unix * 1000));
-    firstFireLabel.append(firstFireInput);
+    form_.append(scheduleField('next fire', firstFireInput));
-    form_.append(firstFireLabel);
 
     const intervalCx = buildIntervalComposer({
       label: 'interval (blank / all-zero = flip to one-shot)',