fix(client-web): reject unknown web kind, lock fixture to contract, observe web card in boot smoke

- webCardModel returns null for an unknown web `kind` (wire from a newer host)
  instead of drawing it as a malformed fetch, matching the unknown-`card` and
  terminal-model wire-boundary default.
- Fixture WEB_SEARCH_RESULT/WEB_FETCH_RESULT and the source type derive from the
  contract's ToolResultView via Extract, so a new contract field fails at the
  type level rather than drifting silently.
- built-boot smoke asserts the web_search/web_fetch turns render their keyed
  WebRow cards, giving the registration and wire projection an assembled check.
- DetailsPanel comment no longer claims the card omits content for search.
- ui-primitives README inline-Chinese limitation now lists WebBlock's controls.

packages/client/ui-conversation/tests/web-card.spec.tsx

@@ -105,6 +105,10 @@ describe('webCardModel', () => {
     // documented generic-card default takes it, not a crash.
     const future = { card: 'chart', kind: 'search' } as unknown as ToolResultView
     expect(webCardModel(settledSearch({ resultView: future }))).toBeNull()
+    // A web card whose kind this UI version does not know (a newer host's
+    // value) also takes the generic path, not a malformed fetch.
+    const futureKind = { card: 'web', kind: 'timeline' } as unknown as ToolResultView
+    expect(webCardModel(settledSearch({ resultView: futureKind }))).toBeNull()
   })
 })