feat(settings): reorder App Settings, tighten the rows, add a live layout preview

The document side of the settings modal was wider than it needed to be: every
row is text on the left and a switch pinned to the right, so a 960px shell plus
a 62ch cap on the description left a dead gap of ~350px between the two. The
shell is now 840px, the rail 196px, and descriptions run to 78ch, which closes
the gap and makes the right side sit proportionally with the rail.

Section order now leads with what you look at first: System (the version this
install runs and whether an update is waiting, with Updates promoted above
Paths/Automation/Remote access), then Terminal & Input, then Header & Panels.
The modal opens scrolled to System instead of Terminal & Input.

Header & Panels gains two things:

- every chip carries the icon of the button it switches on, so the list reads
  as the header itself rather than as a column of names (File Viewer shows the
  folder button, Cron the clock, and so on);
- a live preview above the chips: a scale model of the app with a header bar,
  right-docked panels, a toolbar and floating windows, rebuilt on every chip
  change so "what does this add" is answered in place, before saving.

The preview owns no icons of its own - it CLONES `.set-chip-ico` out of the
chip - so each icon has exactly one copy in index.html and a chip can never
drift from the button it previews. A chip joins the preview by carrying
`data-preview` (which slot) and `data-preview-order` (where in it); readouts
that are not buttons (plan usage, CPU, font size) use `data-preview-text`
instead. The frame is painted from skin tokens only, since hardcoded black
alphas turned it into a grey slab on the four light skins, and it is marked
`data-i18n-skip`: the mock tab names are decoration, and the labels inside are
copies of chip text i18n has already translated.

Cron moved into its own Scheduling group (it is a toolbar button, not a header
one, and the preview places it accordingly).

test/app-settings-structure.test.ts pins the new contract: the rail and the
document agree on order, System leads with the version above the paths, and
every previewed chip has both an icon to clone and a slot that exists.

src/web/public/settings-ui.js

@@ -503,8 +503,10 @@ Object.assign(CodemanApp.prototype, {
     this._syncSettingsChips();
     this._syncModelCards();
     this._syncEffortSegment();
-    // Back to the top of the document (one scroll, not a tab reset).
-    this.switchSettingsTab('settings-terminal');
+    // Back to the top of the document (one scroll, not a tab reset). System is
+    // first now: the version this install is running, and whether an update is
+    // waiting, are the two things worth seeing before anything is configured.
+    this.switchSettingsTab('settings-system');
     const modal = document.getElementById('appSettingsModal');
     modal.classList.add('active');
 
@@ -692,6 +694,79 @@ Object.assign(CodemanApp.prototype, {
     document.querySelectorAll('#appSettingsModal .set-chip').forEach(chip => {
       chip.classList.toggle('is-on', !!chip.querySelector('input')?.checked);
     });
+    this._syncLayoutPreview();
+  },
+
+  /**
+   * Redraw the Header & Panels live preview from the chips above it.
+   *
+   * The preview is a scale model of the app, not a second list of settings, so
+   * every icon is CLONED from the chip that owns it (`.set-chip-ico`): each icon
+   * has exactly ONE copy in index.html and a chip can never drift from the button
+   * it previews. A chip joins the preview purely by carrying `data-preview`
+   * (which slot) and `data-preview-order` (where in that slot); nothing here
+   * needs to know the setting's name.
+   *
+   * `data-preview-text` replaces the icon with a text token for the header
+   * entries that are readouts rather than buttons (plan usage, CPU, font size).
+   */
+  _syncLayoutPreview() {
+    const modal = document.getElementById('appSettingsModal');
+    if (!modal || typeof modal.querySelectorAll !== 'function') return;
+    const slots = {
+      header: document.getElementById('appSettingsPreviewHeader'),
+      panel: document.getElementById('appSettingsPreviewPanels'),
+      toolbar: document.getElementById('appSettingsPreviewToolbar'),
+      float: document.getElementById('appSettingsPreviewFloats'),
+    };
+    if (!slots.header) return;
+    Object.values(slots).forEach(el => {
+      if (el) el.innerHTML = '';
+    });
+
+    const chips = [...modal.querySelectorAll('.set-chip[data-preview]')]
+      .filter(chip => chip.querySelector('input')?.checked)
+      .sort((a, b) => (Number(a.dataset.previewOrder) || 0) - (Number(b.dataset.previewOrder) || 0));
+
+    let shown = 0;
+    for (const chip of chips) {
+      const kind = chip.dataset.preview;
+      const slot = slots[kind];
+      if (!slot) continue;
+      // The label is the chip's own text; the icon span (if any) is skipped by
+      // taking the LAST span, which is always the label.
+      const spans = chip.querySelectorAll('span');
+      const label = (spans[spans.length - 1]?.textContent || '').trim();
+      const el = document.createElement('span');
+      el.title = label;
+      if (kind === 'header') {
+        const text = chip.dataset.previewText;
+        el.className = text ? 'set-preview-chip' : 'set-preview-btn';
+        if (text) el.textContent = text;
+        else this._appendPreviewIcon(el, chip);
+      } else {
+        el.className = `set-preview-${kind}`;
+        this._appendPreviewIcon(el, chip);
+        const name = document.createElement('span');
+        name.textContent = label;
+        el.appendChild(name);
+      }
+      slot.appendChild(el);
+      shown++;
+    }
+
+    const empty = document.getElementById('appSettingsPreviewEmpty');
+    if (empty) empty.hidden = shown > 0;
+  },
+
+  /** Clone a chip's icon into a preview element (see _syncLayoutPreview). */
+  _appendPreviewIcon(target, chip) {
+    const icon = chip.querySelector('.set-chip-ico');
+    if (!icon) return;
+    const clone = icon.cloneNode(true);
+    clone.classList.remove('set-chip-ico');
+    clone.classList.add('set-preview-ico');
+    target.appendChild(clone);
   },
 
   /**
@@ -860,6 +935,10 @@ Object.assign(CodemanApp.prototype, {
       section.classList.toggle('set-hit-hidden', !!q && !hasVisible);
     });
 
+    // The live preview sits outside any group, so it survives the sweep above;
+    // a search is asking for one row, not for the scale model around it.
+    doc.querySelectorAll('.set-preview').forEach(pv => pv.classList.toggle('set-hit-hidden', !!q));
+
     const empty = document.getElementById('appSettingsSearchEmpty');
     if (empty) empty.hidden = !q || anyVisible;
     if (!q) doc.querySelectorAll('.set-group-advanced').forEach(g => g.classList.remove('open'));