feat(telegram): 优化Telegram文件下载与base64转换逻辑，重构消息发送相关代码

- 新增 TelegramModule.download_file_to_base64 方法，统一文件下载与base64编码
- Telegram 客户端新增 download_file 方法，简化文件下载流程
- 消息图片下载逻辑调整为通过模块方法调用，移除冗余静态方法
- 修复部分参数格式与空格风格，提升代码一致性
- 优化长消息发送异常处理与代码结构

app/modules/telegram/__init__.py

@@ -288,7 +288,7 @@ class TelegramModule(_ModuleBase, _MessageBase[Telegram]):
 
         # Remove mention at the beginning with optional following space
         if cleaned.startswith(mention_pattern):
-            cleaned = cleaned[len(mention_pattern) :].lstrip()
+            cleaned = cleaned[len(mention_pattern):].lstrip()
 
         # Remove mention at any other position
         cleaned = cleaned.replace(mention_pattern, "").strip()
@@ -525,3 +525,23 @@ class TelegramModule(_ModuleBase, _MessageBase[Telegram]):
                     f"Command set has changed, Updating new commands: {filtered_scoped_commands}"
                 )
             client.register_commands(filtered_scoped_commands)
+
+    def download_file_to_base64(self, file_id: str, source: str) -> Optional[str]:
+        """
+        下载Telegram文件并转为base64
+        :param file_id: Telegram文件ID
+        :param source: 来源名称
+        :return: base64编码的图片数据
+        """
+        config = self.get_config(source)
+        if not config:
+            return None
+        client = self.get_instance(config.name)
+        if not client:
+            return None
+        file_content = client.download_file(file_id)
+        if file_content:
+            import base64
+
+            return base64.b64encode(file_content).decode()
+        return None