Add recency and cycle sorting to /memory-skills

[chandra447]

Summary

• sort extension-managed skills in /memory-skills by updated desc, then created desc by default
• add an in-modal s key to cycle sort mode between Updated, Created, and Name
• show the active sort mode in the modal status line and help text

Why

This is a follow-up to the skill review feedback in #32 around making newer or recently touched skills easier to find and review.

Testing

• npm run check
• npx tsx --test tests/handlers/skills-command.test.ts tests/store/skill-store.test.ts