feat(web): render web_search/web_fetch output as a web card

Consume the card:'web' result view (structured sources + answer for search, the
URL and HTTP status for fetch) the web backend PR added. WebBlock
(ui-primitives) draws both kinds via the kind discriminant: a citation list of
safe external links (the MarkdownText protocol allowlist, title-or-hostname
label), a truncation indicator, a height cap matching TerminalBlock; a fetch
summary for the other kind. web-card-model is the single resultView derivation;
a keyed WebRow registers under web_search and web_fetch with the card resident
under its summary. The generic fallback and the details panel are web-aware.
Fixture gains web_search and web_fetch turns for the built-boot snapshot.

packages/client/ui-conversation/src/client/chat/GenericToolCard.module.css

@@ -0,0 +1,15 @@
+/* The generic card grows a resident web card under its summary row when the
+   tool declares the `web` render intent but has no keyed row of its own (the
+   web_search/web_fetch rows register their own WebRow). A column around the
+   ToolRow keeps the row's own 24px height. */
+
+.card {
+  display: flex;
+  flex-direction: column;
+}
+
+/* Row indentation matches ToolRow's expanded bodies (16px leading + 6px gap),
+   and replaces the primitive's standalone vertical margin with the flow's. */
+.web {
+  margin: 4px 0 4px 22px;
+}