feat(web): W4-F rebuild agent conversation and drawer with agentui components

- Port agentui (MIT, ashish200729/agentui@b2b752b) Message/MessageBubble/MessageScroller,
  StreamingResponse, ToolResult/ToolApproval, TodoList, ApprovalCard, CodeBlock/FileDiff,
  Citations, PromptInput into components/agentui; drop motion/shiki/Next, switch colors,
  type scale, radii, durations and easing to semantic tokens, honour reduced motion
- Conversation: streaming cursor, collapsible thinking, tool cards with kind/scope/risk/
  idempotency badges and audit idempotency key, prominent server-rejection state for both
  whitelist rejections and unauthorized errors, compaction markers, budget meters with
  over-limit state, approval cards (admin session only), two-column final report
  (model said vs system verified with task/record links), follow-scroll with jump-to-bottom
- Composer: Enter send / Shift+Enter newline, stop = abort (confirmed), append,
  execute/plan_only switch, "execute this plan" from finished plan_only runs
- Session list sidebar with status filter and usage; reconnect/error banners with retry
- Drawer: route-derived context (entity/site/task), minimize to a live mini dock
- Fix stream refetch race when the run switches from loading to finished

Co-Authored-By: Claude Opus 5.5 <[email protected]>

apps/web/app/components/agentui/use-reduced-motion.ts

@@ -0,0 +1,21 @@
+// Adapted from agentui (https://github.com/ashish200729/agentui) — replaces `useReducedMotion` from motion/react.
+// Copyright (c) 2026 Saurabh Chauhan. MIT License, see ./LICENSE-agentui.md
+// 改造:不引 motion 库,直接读 prefers-reduced-motion;样式层的减弱动效由 motion-reduce: 变体负责,这里只给 JS 滚动用。
+import { useSyncExternalStore } from "react";
+
+const QUERY = "(prefers-reduced-motion: reduce)";
+
+function subscribe(cb: () => void) {
+  if (typeof window === "undefined" || !window.matchMedia) return () => {};
+  const mq = window.matchMedia(QUERY);
+  mq.addEventListener("change", cb);
+  return () => mq.removeEventListener("change", cb);
+}
+
+export function useReducedMotion(): boolean {
+  return useSyncExternalStore(
+    subscribe,
+    () => (typeof window !== "undefined" && window.matchMedia ? window.matchMedia(QUERY).matches : false),
+    () => false,
+  );
+}