Fill a selected row written by hand in secondary-container again

1.x drew `data-selected` on any `data-list-row` that was not a card in
secondary-container with on-secondary-container ink, whatever element
the row was. 2.0.0 kept that only for `<x-list-item selected>` and a
table row's `aria-selected="true"`, so an application's own `<li>`,
`<div>` or `<tr>` with `data-md-list-row` and `data-md-selected` - the
contract list-rows.js still describes - lost its selected state without
a word. list-item.css now fills such a row, cards and list items
excluded, and names the fill `--md-list-row-fill`, so hover, focus and
press tint it as they tint a selected list item rather than replacing
it (1.x's selected fill hid them). In `<x-table>`, `data-md-selected`
selects a plain row too, beside `aria-selected="true"`, which ARIA
allows on a row only in a grid. A browser test compares a hand-made
selected `<li>` and a plain selected `<tr>` with the role pair in the
light and dark themes, checks that a selected card keeps its own fill
and that hover tints the row's fill; it fails without the change.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

UPGRADE.md

@@ -17,6 +17,12 @@
   family now too: `border-collapse`, `border-spacing-*`, `from-10%`, `via-none`, `fill-none`,
   `stroke-*`, `text-shadow-*`, `text-inherit`, and Tailwind 4.2's `mauve`, `olive`, `mist` and
   `taupe` palettes. A test that expects no findings may fail on them.
+- **A selected row written by hand** — `data-md-list-row` with `data-md-selected` on an `<li>`, a
+  `<div>` or a `<tr>`, not `<x-list-item>` or `<x-card>` — is drawn in `secondary-container` with
+  `on-secondary-container` ink again, as 1.x's `data-list-row` with `data-selected` was; 2.0.0
+  dropped the fill without saying so. Hover, focus and press now tint the fill instead of hiding
+  it. In `<x-table>` a plain row takes `data-md-selected` too, beside `aria-selected="true"`. A
+  card still takes no selected fill.
 
 ## From 2.0.0 to 2.1.0