feat(tg): 思考块改为可折叠引用块（与工具调用区分）

TG 不支持按消息自定义引用块颜色（竖线颜色跟随客户端主题），按用户
选择采用官方可折叠引用块：默认收起为「💭 思考过程 ▾」，点击展开，
与工具调用的普通蓝色竖线引用块在交互上明确区分。

- rich 模式：Telegram 原生 markdown 可折叠引用语法（**> 开头 + 行尾 ||）
- HTML 模式：markdownToHtml 转换为 <blockquote expandable>
- 思考文本内的 || 全角化，避免被解析成 spoiler 实体

lib/format.js

@@ -12,22 +12,54 @@ function inlineToHtml(text) {
     html = html.replace(/\*\*([^*\n]+)\*\*/g, '<b>$1</b>');
     return html;
 }
-/** Convert `> …` line groups into `<blockquote>` (Telegram renders it with the accent-colored left bar). */
+/**
+ * Convert `> …` line groups into `<blockquote>` (Telegram renders it with the
+ * accent-colored left bar). The native-markdown expandable-quote form
+ * (`**>first line` … `last line||`) becomes `<blockquote expandable>` — used
+ * for thinking blocks so they stay collapsed and distinct from tool-call
+ * quotes (Telegram has no per-message quote color).
+ */
+const EXPANDABLE_OPEN = '**>';
 function blocksToHtml(text) {
     const lines = text.split('\n');
     const out = [];
     let quote = [];
+    let expandable = false;
     const flush = () => {
         if (quote.length === 0)
             return;
-        out.push(`<blockquote>${inlineToHtml(quote.join('\n'))}</blockquote>`);
+        const open = expandable ? '<blockquote expandable>' : '<blockquote>';
+        out.push(`${open}${inlineToHtml(quote.join('\n'))}</blockquote>`);
         quote = [];
+        expandable = false;
     };
     for (const line of lines) {
-        if (line.startsWith('> '))
-            quote.push(line.slice(2));
-        else if (line === '>')
+        if (line.startsWith(EXPANDABLE_OPEN)) {
+            flush();
+            expandable = true;
+            let content = line.slice(EXPANDABLE_OPEN.length);
+            if (content.endsWith('||')) {
+                quote.push(content.slice(0, -2));
+                flush();
+            }
+            else {
+                quote.push(content);
+            }
+        }
+        else if (line.startsWith('> ')) {
+            let content = line.slice(2);
+            let closed = false;
+            if (expandable && content.endsWith('||')) {
+                content = content.slice(0, -2);
+                closed = true;
+            }
+            quote.push(content);
+            if (closed)
+                flush();
+        }
+        else if (line === '>') {
             quote.push('');
+        }
         else {
             flush();
             out.push(inlineToHtml(line));