fix: rewrite skill.md from agent-first perspective

Refocus skill.md on what AI agents actually need: MTLAX registration
via trustline, stellar-cli identity setup with hex-encoded examples,
and API querying. Remove human-only content (membership levels,
Telegram bot join flow, family relationships).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: xdefrag