feat: group settings, invite management, profile picture, disappearing

[longevityboris]

Complete group management with remaining features:

• join_group_with_link(invite_code) — join a group via invite link
• revoke_group_invite_link(group_jid) — reset invite link (pass reset: true)
• set_group_settings(group_jid, announce: bool, locked: bool) — toggle who can send/edit
• set_group_picture(group_jid, image_data) — set group profile picture
• set_disappearing_messages(group_jid, duration) — enable/disable disappearing messages

Part of group management parity with Baileys.