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-TW.json

@@ -1220,7 +1220,7 @@
       "telegramAPIServer": "Telegram API 伺服器",
       "telegramAPIServerDesc": "要使用的 Telegram API 伺服器。留空以使用預設伺服器。",
       "telegramChatId": "管理員聊天 ID",
-      "telegramChatIdDesc": "Telegram 管理員聊天 ID (多個以逗號分隔)（可通過 {'@'}userinfobot 獲取，或在機器人中使用 '/id' 命令獲取）",
+      "telegramChatIdDesc": "Telegram 管理員聊天 ID (多個以逗號分隔)（可通過 {'@'}userinfobot 獲取，或在機器人中使用 '/id' 命令獲取） 如需發送到論壇話題，請追加 ':topicId'，例如 -1001234567890:42",
       "telegramNotifyTime": "通知時間",
       "telegramNotifyTimeDesc": "Telegram 機器人傳送週期性報告的頻率。選擇預設間隔，或選擇「自訂」以輸入 crontab 運算式。",
       "notifyTime": {