Flatten the selection and the menu highlight; kill the Aero afterglow

Three things looked wrong, three different causes.

The selected row carried a border. 7.css outlines tr.highlighted (#aaddfa) on
top of its fill, and we had been restating that outline in the new blue — so
the band had an edge, and on the cursor row the dotted focus rect made three
concentric outlines around a single row. The reserved 1px border stays (it is
what stops selection from shifting rows) but is transparent in every state;
the fill paints under it, since background-clip is border-box. --w7-sel-bd and
--w7-sel-bd-idle are gone with it.

The context menu highlighted items with 7.css's translucent gradient wash —
the same gradient the ListView selection just dropped. It now uses
--w7-sel-bg, so selection reads identically wherever it appears.

The hover-off animation was button.css bleeding into menu items, which ARE
buttons: button::before is a glow overlay that fades out over a full second,
and menu.css suppresses it with content:none on the :hover arm ONLY — so
leaving an item brought the pseudo back with opacity animating 1 -> 0, a ghost
trailing the pointer. Killing content in every state removes it. Same family,
also fixed: button:focus runs pulse-anim infinitely, and this menu moves real
focus between items for keyboard nav.

menu-probe.ts now checks the highlight too, using hover-probe's :hover ->
.simhover rewrite: it measures colour spread down a text-free strip of a
force-hovered item, so "is it flat?" is a measurement. Verified the check can
fail by injecting the old wash into the built stylesheet — spread 9, exit 2;
the flat fill reads spread 0 at exactly #cbe8f6. The harness lost its
selection outlines and nothing else, in both themes.

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

ui/dev/harness.html

@@ -200,7 +200,10 @@
       </figure>
       <figure class="cell" style="margin:0">
         <figcaption>ours — context-menu.ts output (buttons, divider, accelerator, checkables)</figcaption>
-        <ul role="menu" style="width:200px">
+        <!-- w7-ctx is the app's marker class (flat highlight, no Aero afterglow).
+             It also carries a position:fixed restatement, which the app wants and a
+             review page in normal flow does not — hence the inline static. -->
+        <ul role="menu" class="w7-ctx" style="width:200px;position:static">
           <li role="menuitem"><button type="button">Send to Other Panel</button></li>
           <li role="menuitem"><button type="button">Open</button></li>
           <li role="menuitem"><button type="button">Edit <span>F4</span></button></li>