fix: save expired TTL messages deleted via auto-delete in groups

[denfry]

Summary

• When a group has auto-delete enabled, messages receive a ttlDestroyAt timestamp
• If the app restarts (or messages are scrolled into view) after the TTL has already expired, applyTTL takes the now >= _ttlDestroyAt branch and schedules item->destroy() via crl::on_main — bypassing processMessageDelete entirely
• This means AyuGram never gets a chance to save the message to the deleted messages database

Fix

Replace item->destroy() with processMessageDelete(item) in the expired-TTL path of applyTTL. telegram_helpers.h (which declares processMessageDelete) was already included in history_item.cpp.

Closes #300

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