Add a platform-aware route target system so a single route can forward
to several destinations at once (e.g. a Discord channel and a Telegram
group). Route.target becomes Route.targets[] with per-entry platform,
channelId/threadId for Discord and chatId/topicId for Telegram; the
legacy single-target format is normalized on load and accepted by the
admin API.
Implement the Telegram driver with HTML rendering and Bot API
sendMessage (chat_id + message_thread_id for topics, retry on 429/5xx),
plus /gh commands served over POST /telegram/webhook: login, logout,
comment, merge and close. The comment/merge/close commands resolve the
issue or PR from the replied-to notification message. OAuth binding now
stores a D1 telegram_links mapping and replies with a confirmation.
Sync the Telegram webhook from the scheduled trigger via setWebhook.
