fix(web-cards): restore AT status text, guard file-link keys, add read docs

Address review of the ToolRow card refactor:
- ToolRow renders a visually-hidden run-state label (row.running/failed/stopped
  locale keys) so a running/failed/interrupted row is not a colour-only signal;
  the StateDot and the sweep are both aria-hidden. Restores the stopped-state
  text assertion in diff-card.spec at the ToolRow layer.
- The file-link button stops Enter/Space from bubbling to DisclosureRow's
  whole-row keydown, which would preventDefault the key and toggle expand
  instead of opening the file (the keyboard analogue of the click stopPropagation).
- search-row passes output={model.output} unconditionally, matching the other
  three card rows (ToolRow renders the card over the output when present).
- Assert locale: 'conversation' in the search/web/diff registration tests.
- Add the read render-intent paragraph to the ui-conversation README and a
  ReadBlock atom entry + Read section to ui-primitives (both languages).
- Update the grep fixture sample lines to the post-refactor SearchRow shape.
Refresh the code-mode-round, steering, and search-card goldens for the added
status text and updated sample lines.

apps/web/tests/snapshots/code-mode-round/ui.expected.md

@@ -24,7 +24,7 @@
   - img
   - text: Code Run bash echo and catch missing file read
 - img
-- text: Bash Echo CODE_ROUND_OK
+- text: Bash Echo CODE_ROUND_OK Failed
 - 'button "Read Error: cannot read \"{{cwd}}/workspace/missing.txt\": not found"':
   - img
   - text: "Read Error: cannot read \"{{cwd}}/workspace/missing.txt\": not found"