docs: improve skill metadata and navigation

[joneidejohnsen]

Why

These changes align the repo more closely with Anthropic's published skill best practices: Anthropic Skill Creator guide.

The main reasons for the update are:

• improve skill triggering by moving more concrete task language into each skill's description, since name and description are the primary discovery fields
• simplify SKILL.md frontmatter to the portable name + description shape used in Anthropic's public skill format
• make long reference docs easier for agents to scan with lightweight tables of contents, which supports the guide's progressive-disclosure approach
• clean up repo docs so examples and contributor guidance match the actual skill layout and current usage patterns

Summary

• align all four skills with stronger trigger-oriented descriptions and simplify SKILL.md frontmatter to the portable name + description shape
• add table-of-contents navigation to the longest reference docs so agents can jump to the relevant sections faster
• update README.md and /sanity command copy so the repo docs reflect the current skill layout and contributor workflow

Test plan

• npm ci
• npm run validate:all