feat: single-page documentation type

[oto-macenauer-absa]

feat: single-page documentation type (#35)

Closes #35.

Adds a third onboarding type to the knowledge base: single-page — zero-config documentation published straight from plain markdown. A docs repo onboards by adding a single workflow file; no mkdocs, no build config, no manifest files.

Reusable action — actions/publish-single-page-docs

• Input: a docs list (YAML) — each entry md, title, description, slug, optional icon + tags
• Renders markdown → headless HTML inside the action: GFM (tables, task lists, footnotes, autolinks), syntax highlighting (light theme per contract/STYLE_GUIDE.md), Mermaid diagrams (vendored, no CDN — pages stay self-contained)
• Packs one bundle dist.tar.gz (subdir per slug + bundle.json manifest) and uploads it to the repo's latest release (--clobber); optional release-tag input defaults to the triggering release
• Self-contained dependency tree (own package.json/lockfile), covered by a new CI self-test job

Knowledge base

• apps.json entry: { "repo": "org/repo", "type": "single-page" } — no per-doc metadata; the build reads bundle.json and expands the entry into one app per doc (slug-collision guarded, expansion recorded in apps/.single-page.json and spliced back via loadRegistry() so Astro sees what the build saw)
• Rendering: masthead as everywhere, no sidebar, content in a centred main.mp-single-page reading column, light-only
• prebuilt bundles supported for hermetic/offline builds; registry entries may be "optional": true (skip-with-warning when the local artifact is absent — keeps CI green while enabling local visual testing against a sibling example repo)

Onboarding (copy-paste for a docs repo)

# .github/workflows/publish-docs.yml
on:
  release:
    types: [published]
  workflow_dispatch:
jobs:
  publish:
    runs-on: ubuntu-latest
    permissions:
      contents: write
    steps:
      - uses: actions/checkout@v4
      - uses: AbsaOSS/knowledge-base/actions/publish-single-page-docs@master
        with:
          docs: |
            - md: docs/overview.md
              title: Service Overview
              description: What the service does and how to use it.
              slug: my-service

Docs & tests

• New contract/SINGLE_PAGE.md (bundle format + onboarding guide); README, CLAUDE.md, contract/HEADLESS_RULES.md updated
• Hermetic single-page fixture; +8 build-integrity and +3 web-fragment tests
• Suites: 43/43 embedded, 15/15 standalone, 11/11 action self-test

Notes for reviewers

• Mermaid rendering inside the reframed web-fragment shadow DOM is asserted at asset/markup level only (source survives, vendored JS resolves, no CDN); an actual draw-test would require the full 2.5 MB bundle in the fixture
• A local sibling repo knowledge-base-example-single-page (not part of this PR) exercises the real action output visually via npm run build:local && npm run preview

🤖 Generated with Claude Code

https://claude.ai/code/session_01CRZk4ZQsApxLANJtzQpVXb

Release Notes

• Add reusable GitHub workflow for smooth single page docs onboarding
• Add new type of documentation - single page