feat(marketing): add x-twitter-growth skill with 5 Python tools
- Profile auditor (bio quality, posting patterns, growth readiness)
- Tweet composer (hooks, threads, validation, 30+ proven patterns)
- Content planner (weekly calendars with format mix)
- Competitor analyzer (competitive intel via data import)
- Growth tracker (snapshot-based progress tracking + milestone projection)
- Algorithm reference doc (ranking signals, timing, format performance)
- 226-line SKILL.md with practical playbook (no fluff)
- Security audit: PASS (0 findings)
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