Add HTML Docs authoring skill release artifact

[yolo-sam]

Summary

• update the HTML Docs authoring skill against merged theme-token injection from PR feat: Inject Obsidian theme tokens into HTML docs #8
• bundle the canonical skill into release output as dist/html-docs/SKILL.md
• include the bundled skill in release upload and provenance attestation
• document optional agent-skill install/discovery in README, including the skills.sh install command

Ownership / discovery

• canonical source: this repo, .agents/SKILL.md
• installable mirror: smcllns/skills, skill obsidian-html-docs
• smcllns/skills PR Not listed in Obsidian Community plugins #1 is merged, so the README now points at the real install command:
  bunx skills add smcllns/skills --skill obsidian-html-docs
• Obsidian plugin install/update does not activate Claude/Codex skills because agents discover skills from their own configured roots, not vault plugin folders
• plugin runtime does not write to agent install roots, dotfiles, or user-level configuration

Merge order

• Done: merge smcllns/skills PR Not listed in Obsidian Community plugins #1 first so the public install target exists
• Next: merge this PR Add HTML Docs authoring skill release artifact #7
• Then: cut the next plugin release so dist/html-docs/SKILL.md is attached as a reference artifact

Verification

• bun run build
• bun run lint
• bun run test against live Obsidian before the docs-only install-command follow-up
• diffed .agents/SKILL.md against generated dist/html-docs/SKILL.md
• diffed .agents/SKILL.md against smcllns/skills mirror
• Haiku critical review found one light-dark() wording mismatch; fixed
• grepped public docs/source for private local path leaks after review feedback

[smcllns]

LGTM