feat(ui): 强化 AI 工作中动效——构思占位/流式进度条/波动三点/转圈

- 动效基元：ai-dot 波动(三点竖跳)、ai-stream 不确定进度条、ai-breathe 呼吸微光（均带 reduced-motion 回退）
- ThinkingIndicator 升级为明显波动；新增 Spinner / StreamingBar / GenerationSkeleton 原子件；Button 加 loading 态
- 写作台：首 token 前正文区『AI 正在构思本章…』占位（补最大缺口，不再空白像卡死）+ 流式顶部进度条
- 整章重写流式进度条；续写/润色忙碌骨架 + 触发键转圈；生成器/角色/世界观改用 Button loading

apps/web/components/workbench/ContinuePanel.tsx

@@ -3,8 +3,8 @@
 import { useCallback, useEffect, useRef } from "react";
 import { Check, Plus, X } from "lucide-react";
 
-import { ThinkingIndicator } from "@/components/ThinkingIndicator";
 import { Button } from "@/components/ui/Button";
+import { GenerationSkeleton } from "@/components/ui/GenerationSkeleton";
 import { SectionHeader } from "@/components/ui/SectionHeader";
 import { StatusNote } from "@/components/ui/StatusNote";
 import { useContinue } from "@/lib/workbench/useContinue";
@@ -72,12 +72,6 @@ export function ContinuePanel({
         </Button>
       </div>
 
-      {candidates.length === 0 && busy ? (
-        <div className="mt-3">
-          <ThinkingIndicator label="续写中" className="text-xs text-cinnabar" />
-        </div>
-      ) : null}
-
       {candidates.length === 0 && status === "error" ? (
         <StatusNote variant="danger" className="mt-3 text-xs" title="续写失败">
           <button
@@ -112,10 +106,13 @@ export function ContinuePanel({
         ))}
       </ul>
 
+      {/* 续写为同步请求（无逐字流）：生成期间放一块呼吸微光骨架占位，比单三点更明显地示意正在生成。 */}
+      {busy ? <GenerationSkeleton label="续写中" className="mt-3" /> : null}
+
       <div className="mt-3">
         <Button
           onClick={() => void runGenerate()}
-          disabled={busy}
+          loading={busy}
           variant="secondary"
           size="sm"
         >