Stage 2: file panels become a real 7.css ListView

The file list was a CSS grid of <div>s, so 7.css's listview component never
matched a single selector and Tailwind styled the whole thing. It is now the
plain <table> 7.css documents, which is what makes the Aero treatment appear.

- The column header row moved OUT of its own div and INTO <thead>: 7.css makes
  thead position:sticky, so it stays put while the body scrolls, and it has to
  be inside the same table to do that.
- Column widths moved from a computed grid-template-columns to <colgroup>,
  because 7.css sets table-layout: fixed. `gridTemplate()` is deleted.
- Selection is now `tr.highlighted` (7.css's gradient band + #aaddfa border)
  instead of bg-primary/15.
- The sort arrow was the text glyph ↑/↓ from `sortIndicator()`, which is also
  deleted; the sorted column is now `th.highlighted.indicator[.up]` and 7.css
  draws the real clip-path triangle in the header.
- Row height, padding, borders and fonts now come from 7.css, so --row-h and
  the per-cell text/color/font utilities are gone.

Two things 7.css does not cover, added in `skinfix`:
- Dark mode. listview.css hardcodes light literals (#fff, #c0c1cd, #eee and a
  white header gradient) rather than --w7-* vars, so it does NOT follow the
  hand-authored dark palette — the header labels rendered invisible, dark on
  dark. The dark arms restate those rules; light keeps 7.css's own values.
- The keyboard cursor. 7.css models selection only; Win7 drew the focused row
  with a dotted focus rectangle over it, which is what tells "cursor" apart
  from "selected" when they differ. That is `tr.is-cursor`.

Verified visually this time, not just by build log: harness screenshots in both
light and dark show the header gradient, sort triangle, cell separators,
selection band and cursor rectangle matching 7.css's reference markup. Backend
`tsc --noEmit` clean, `bun run build:ui` clean, bundle 489.83 kB (from 490.50).

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

ui/dev/harness.html

@@ -91,17 +91,27 @@
         </table>
       </figure>
       <figure class="cell" style="margin:0">
-        <figcaption>ours — div grid (7.css never applies)</figcaption>
-        <div style="border:1px solid var(--w7-el-bd); background:#fff">
-          <div style="display:grid;grid-template-columns:1fr 5.5rem 8.5rem;font-size:11px;opacity:.7;border-bottom:1px solid #d7d7d7">
-            <div style="padding:2px 8px">Name</div>
-            <div style="padding:2px 8px;text-align:right">Size</div>
-            <div style="padding:2px 8px">Modified</div>
-          </div>
-          <div style="display:grid;grid-template-columns:1fr 5.5rem 8.5rem"><div style="padding:2px 8px">..</div><div style="padding:2px 8px;text-align:right">—</div><div style="padding:2px 8px">—</div></div>
-          <div style="display:grid;grid-template-columns:1fr 5.5rem 8.5rem"><div style="padding:2px 8px">Documents</div><div style="padding:2px 8px;text-align:right">—</div><div style="padding:2px 8px">3/29/2007</div></div>
-          <div style="display:grid;grid-template-columns:1fr 5.5rem 8.5rem;background:rgba(59,130,246,.15)"><div style="padding:2px 8px">report.pdf</div><div style="padding:2px 8px;text-align:right">27 KB</div><div style="padding:2px 8px">3/23/2007</div></div>
-        </div>
+        <figcaption>ours — file-panel.html (selected + cursor row)</figcaption>
+        <table>
+          <colgroup>
+            <col />
+            <col style="width: 5.5rem" />
+            <col style="width: 8.5rem" />
+          </colgroup>
+          <thead>
+            <tr>
+              <th>Name</th>
+              <th class="highlighted indicator up" style="text-align:right">Size</th>
+              <th>Modified</th>
+            </tr>
+          </thead>
+          <tbody>
+            <tr><td>..</td><td style="text-align:right">—</td><td>—</td></tr>
+            <tr><td>Documents</td><td style="text-align:right">—</td><td>3/29/2007 12:00 AM</td></tr>
+            <tr class="highlighted"><td>report.pdf</td><td style="text-align:right">27 KB</td><td>3/23/2007 12:00 AM</td></tr>
+            <tr class="is-cursor"><td>notes.txt</td><td style="text-align:right">4 KB</td><td>3/13/2007 12:00 AM</td></tr>
+          </tbody>
+        </table>
       </figure>
     </div>