feat: profile & privacy (picture, name, bio, block, privacy settings)

[longevityboris]

Add profile and privacy management:

• get_profile_picture(jid) / set_profile_picture(data) — profile picture
• set_profile_name(name) — update push name
• get_about(jid) / set_about(text) — bio/about text
• fetch_privacy_settings() / update_privacy_settings(...) — privacy config
• block_contact(jid) / unblock_contact(jid) — block management
• fetch_blocklist() — get blocked contacts
• get_business_profile(jid) — business account info

Lower priority — most bridge consumers don't need these.