feat(tgbot): route admin notifications to a forum topic (#6879)

Admins who run the bot in a forum supergroup got every notification in the
General topic. An admin chat ID may now carry a topic, chatId:topicId, and the
bot's admin messages and reports go to that topic. Repeated chats collapse into
one entry and a second, different topic for the same chat is rejected, in the
panel and in the docs setup helper alike. The chat ID hint in every locale and
the English, Persian, Russian and Chinese guides describe the form.

internal/web/translation/zh-CN.json

@@ -1220,7 +1220,7 @@
       "telegramAPIServer": "Telegram API 服务器",
       "telegramAPIServerDesc": "要使用的 Telegram API 服务器。留空以使用默认服务器。",
       "telegramChatId": "管理员聊天 ID",
-      "telegramChatIdDesc": "Telegram 管理员聊天 ID (多个以逗号分隔)（可通过 {'@'}userinfobot 获取，或在机器人中使用 '/id' 命令获取）",
+      "telegramChatIdDesc": "Telegram 管理员聊天 ID (多个以逗号分隔)（可通过 {'@'}userinfobot 获取，或在机器人中使用 '/id' 命令获取） 如需发送到论坛话题，请追加 ':topicId'，例如 -1001234567890:42",
       "telegramNotifyTime": "通知时间",
       "telegramNotifyTimeDesc": "Telegram 机器人发送周期性报告的频率。选择预设间隔，或选择“自定义”以输入 crontab 表达式。",
       "notifyTime": {