v3.0.0 - Progressive disclosure for skills: SKILL.md + references/ (v3.0.0)

• all skills: Skills now use progressive disclosure: SKILL.md keeps the guide header, Section 0, and an index with a one-line "when to read" summary per section, and every other section moves to references/<slug>.md. A triggered skill loads about 50 lines instead of up to 1,370, in line with the Agent Skills 500-line guidance. Cross-section links are rewritten to the right reference file
• aws-spa-deploy, seo-llmo: "See above/below" pointers that now cross reference files are links, so they still work when a section is read on its own. Guide content is otherwise unchanged and the guides remain single files
• CLI: init --skills installs the whole skill, including references/, and swaps the generated files in only once every file is written, so a failed install never leaves a half-updated skill; other files in the skill folder are kept. The Done message reports failures, and the GitHub fallback prints build warnings
• CI: Fails on untracked files under skills/ (not only modified ones) and runs a new check:skills validator for line limits, broken links or anchors, and orphaned reference files