v3.0.1

Fix skill descriptions to match Agent Skills spec

• Remove YAML block scalars (| and >) from all skill description fields — use plain strings per the Agent Skills specification
• Restructure descriptions to lead with proactive use guidance, followed by trigger keywords, then base description
• Affects all 8 skills: modern-css, mermaid-diagrams, modern-javascript, postgres-drizzle, clean-ddd-hexagonal, feature-slicing, slack-mrkdwn, slack-block-kit