v1.60.2

Changed

• Internal groundwork (v2): the update lock — the single mutex that coordinates the scheduler, the Web UI and the bot so two updates never run at once — now lives on a new UpdateEngine instead of the Telegram bot, mirrored back onto the bot by property so every existing caller still sees the exact same lock object. Pure aliasing, no behaviour change; it's the first, deliberately smallest step of moving the update orchestration out of the Telegram bot so a second interface (a Discord bot, later) can share it. The riskier pieces follow one at a time.