feat(web): render write/edit tool output as a diff card

The write/edit tools already declare card:'diff' with applied hunks on
callView/resultView, but the Web client discarded it: a mutation landed on
GenericToolCard and the details panel flattened the result to a <pre>. Add
DiffBlock (ui-primitives), diff-card-model (the single callView/resultView
derivation), and FileMutationRow (keyed under write and edit), and make the
generic fallback row and the details panel diff-aware. The +/- block form,
per-file path header, same-file gap, and footer mirror the TUI diff card;
the chat row caps at CHAT_DIFF_MAX_LINES against the panel's full height.

packages/client/ui-conversation/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/client/ui-conversation/README.md
-README.md: 3973c14f2b8fe746549bb74af85a7a60a7d66aea
-README.zh.md: a6bb15c4cdd53d05bf28147b97d9d64d1c59da2b
+README.md: d3cd5cc268b60b58bb4dbb6c3b6c118084c0def8
+README.zh.md: f3a835ed82ecbd266b9f0829acc6182209940cb5