feat(skill): Create decision-history skill structure

[yonatangross]

Summary

Create the skill scaffolding for /ork:decision-history - CLI dashboard to visualize OrchestKit decisions tied to Claude Code version evolution.

Tasks

• Create skills/decision-history/SKILL.md with frontmatter (user-invocable: true)
• Create references/ directory
• Create scripts/ directory
• Create assets/decision-schema.json
• Add commands/decision-history.md for autocomplete

Acceptance Criteria

• Skill appears in /ork: autocomplete
• SKILL.md has valid frontmatter
• Directory structure matches 4-tier pattern

Dependencies

None (first issue)

Effort

S (Small) - Scaffolding only

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Related: #46 (milestone)