KtgContextSource
Resolves the KtgContext lazily, once a TelegramBot instance becomes available.
Unlike kotlin-telegram-bot, ktgbotapi hands out the TelegramBot instance up front (telegramBot(token)), so the usual wiring is simply KtgContextSource(bot) — the deferred shape is kept for the cases where the executor has to be built before the bot exists (and to mirror :telegram's TelegramContextSource). Share one instance between ktgEffectExecutor and connect so the executor awaits the same bot the behaviour context observes, without ru.workinprogress.telek.Telek needing to own or track it.