docs: add agent skills for AI coding agents

[dangreen]

Why

AI coding agents working on a Nano Kit app need the API of the released packages and the conventions around it. Pasting the documentation into the skills duplicated the site and drifted from it, and pointing agents at the llms.txt sets pulled in the whole site with articles, anchors and images. A skill now carries only guidance, and the documentation next to it is generated from the same sources the site is built from.

What

• skills/nano-kit-{store,query,intl,platform-web,react,react-router,react-ssr}: SKILL.md with conventions, choices and pitfalls (the store skill marks the low-level APIs as territory for adapters, bindings and tests), plus a generated DOCS.md with the released documentation. Installed with pnpx skills add TrigenSoftware/nano_kit --skill <name>.
• scripts/skills-docs: a private workspace package with the skills-docs CLI. It parses the MDX sources with remark, keeps the tabs a skill prefers (metadata.docs.tabs plus --tabs), converts the Starlight components (Tabs, Code, Aside, Steps, Card) to plain Markdown, unwraps internal links to text unless --site is given, drops the sections named in --drop, and fails with --check when a DOCS.md is stale. The pages of a skill come from metadata.docs.paths in its frontmatter. pnpm skills:docs runs it with the repo settings.
• Site: an Agent Skills page in Getting Started (Introduction pinned first), and articles/** excluded from llms-small.txt.
• README: an Agent Skills section with the list of skills and the install command.
• packages/kida/README.md: the example uses the for_ name.
• pnpm-workspace.yaml adds scripts/*. The lockfile diff also carries pnpm 10.33 re-normalising peer suffixes and linkDirectory entries written by earlier Renovate updates.

Not included: CI does not run pnpm skills:docs --check yet.

Checks

• pnpm skills:docs --check passes, all seven DOCS.md are current.
• oxlint scripts/skills-docs passes.
• pnpm install --frozen-lockfile passes.
• astro build of the website passes, 62 pages.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.33%. Comparing base (fb4365f) to head (e9b92be).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #255   +/-   ##
=======================================
  Coverage   83.33%   83.33%           
=======================================
  Files          98       98           
  Lines        2557     2557           
  Branches      552      552           
=======================================
  Hits         2131     2131           
  Misses        314      314           
  Partials      112      112           

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