Krypton v0.2.0

What changed

• Adds the Krypton Goal Gate reusable GitHub Action.
• Adds PLAN.md, GOAL.md, and EVIDENCE.md goal package templates.
• Adds a Codex repo marketplace file at .agents/plugins/marketplace.json.
• Adds skills.sh install instructions and clearer goal-based workflow positioning.
• Adds a tested local gate script: scripts/check-krypton-goal.py.

Verification

• python3 scripts/check-krypton-goal.py --base-ref HEAD~1
• ./scripts/validate.sh
• HOL Plugin Scanner: 91/100, critical 0, high 0