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

src/format.ts

@@ -14,20 +14,50 @@ function inlineToHtml(text: string): string {
   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: string): string {
   const lines = text.split('\n')
   const out: string[] = []
   let quote: string[] = []
+  let expandable = false
   const flush = (): void => {
     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 === '>') quote.push('')
-    else {
+    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))
     }