docs: zero-conf doc site via docmc + GitHub Pages

[espetro]

Effort: S

Publish docs/ as a browsable site via docmd (zero-config, file-based nav), deployed to GitHub Pages via Actions (upload-pages-artifact + deploy-pages), no branch-commit hack.

Scope

• Drop docs/releases/ (duplicates root CHANGELOG.md)
• Taskfile: docs (dev preview) + docs-build (static build to site/) tasks via npx @docmd/core
• README: add docs-site section + link to published Pages URL
• New .github/workflows/docs.yml: build via task docs-build, deploy via actions/upload-pages-artifact + actions/deploy-pages
• Manual one-time: enable Pages source = GitHub Actions in repo settings

Plan: .claude/plans/craft-a-plan-to-purrfect-platypus.md (local, not committed)