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.

packages/client/connection/src/client/fixture.ts

@@ -190,10 +190,10 @@ const SEARCH_MATCHES_FIXTURE: { path: string; matches: { lineNumber: number; lin
   {
     path: 'packages/client/ui-conversation/src/client/toolviews/search-row.tsx',
     matches: [
-      { lineNumber: 71, line: 'export function SearchRow({ toolName, block }: ToolRowProps) {' },
-      { lineNumber: 73, line: '  const search = searchCardModel(block)' },
-      { lineNumber: 90, line: '        <SearchBlock {...search.card} maxLines={CHAT_SEARCH_MAX_LINES} className={css.search} />' },
-      { lineNumber: 113, line: "    ctx.slots.register({ name: 'conversation.chat.toolview', key: 'grep' }, SearchRow)" },
+      { lineNumber: 33, line: 'export function SearchRow({ toolName, block, inspect, t }: SearchRowProps) {' },
+      { lineNumber: 35, line: '  const search = searchCardModel(block)' },
+      { lineNumber: 52, line: '      search={search}' },
+      { lineNumber: 73, line: "    ctx.slots.register({ name: 'conversation.chat.toolview', key: 'grep', locale: NS }, SearchRow)" },
     ],
   },
 ]