feat(skill): Create gemini-consultation skill
Gemini consultation best practices:
- Consultation structure and header template
- Question types (validation, code review, design, debugging)
- Multi-round consultation patterns (Round 1, Round 2, Thank You)
- File naming conventions for docs/consultations/
- Documenting responses with summaries and conclusions
- Best practices for warm, collegial partner tone
- Consultation checklist (before and after)
Updated SKILLS-INDEX.md with new skill entry.
Chronicler: #68
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