feat: 对话列表显示总数，SOUL 编辑区高度自适应收敛

- 新增 POST /threads/count：与 /threads/search 同一套过滤（标题搜索、
  系统会话排除），仅返回 {total}；ThreadMetaStore 增加 count 方法
  （SQL 走 COUNT(*)，JSON 过滤分批扫描计数）
- 对话页面搜索框下常驻显示「共 N 条对话」，分页条显示 当前页/总页数
  （useThreadsCount，仅随筛选条件变化，翻页不重复请求）
- 智能体右侧 SOUL 预览改为 40vh 上限自适应展开（不再全部展开）；
  详情面板/卡片编辑/创建页的 SOUL 输入框统一为适中高度 + 可拖拽

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend-web/src/pages/ChatsPage.tsx

@@ -22,6 +22,7 @@ import {
 } from "@/components/workspace/workspace-container";
 import { useI18n } from "@/core/i18n/hooks";
 import {
+  useThreadsCount,
   useThreadsPage,
   useToggleThreadFavorite,
   useToggleThreadPin,
@@ -90,6 +91,10 @@ export default function ChatsPage() {
     search: debouncedSearch,
     metadata: pinnedFilter,
   });
+  const { data: totalCount } = useThreadsCount({
+    search: debouncedSearch,
+    metadata: favoriteFilter,
+  });
 
   const pinnedThreads = pinnedData?.threads ?? [];
   const pagedThreads = useMemo(
@@ -98,6 +103,10 @@ export default function ChatsPage() {
   );
   const currentPage = page;
   const hasMore = pageData?.hasMore ?? false;
+  // Page windows are sliced over the raw (pinned-inclusive) row order, so the
+  // page count derives from the raw total as well.
+  const totalPages =
+    totalCount != null ? Math.max(1, Math.ceil(totalCount / PAGE_SIZE)) : null;
 
   const renderThread = (thread: AgentThread) => {
     const pinned = isThreadPinned(thread);
@@ -201,6 +210,11 @@ export default function ChatsPage() {
               value={search}
               onChange={(e) => setSearch(e.target.value)}
             />
+            {totalCount != null && (
+              <div className="text-muted-foreground w-full max-w-(--container-width-md) text-right text-xs tabular-nums">
+                共 {totalCount} 条对话
+              </div>
+            )}
           </header>
           <main className="min-h-0 flex-1">
             <ScrollArea className="size-full py-4">
@@ -231,7 +245,9 @@ export default function ChatsPage() {
                       {t.chats.prevPage}
                     </Button>
                     <span className="text-muted-foreground text-sm tabular-nums">
-                      {currentPage}
+                      {totalPages != null
+                        ? `${currentPage} / ${totalPages}`
+                        : currentPage}
                     </span>
                     <Button
                       variant="outline"

frontend-web/src/pages/NewAgentPage.tsx

@@ -546,7 +546,7 @@ export default function NewAgentPage() {
                     placeholder="写下智能体的人设、边界、工作方式和输出要求"
                     value={soulInput}
                     onChange={(event) => setSoulInput(event.currentTarget.value)}
-                    className="min-h-[45vh] resize-y overflow-y-auto font-mono text-xs"
+                    className="max-h-[50vh] min-h-64 resize-y overflow-y-auto font-mono text-xs"
                   />
                 </div>