Allow `/ban @username` in group chats (without replying)

[viganogabriele]

Currently, per-group bans require replying to the user's message with /ban. This breaks when the bot's auto-moderation deletes the message before an admin can reply — e.g., when a user account continuously posts spam messages that get auto-deleted.

Global ban via /ban_all in bot DM is unreliable for some users, so the per-group fallback is necessary.

Suggested improvement:
Allow /ban @username directly in the group, without requiring a reply to a message.

Related:

• Extend AutoModeration message actions to match /report functionality #116 (AutoModeration actions) — addresses this via a complementary approach (actions in log group)

[viganogabriele]

@lorenzocorallo @toto04 one between #116 and this issue should be resolved asap