docs: API reference and getting-started guide for developers.pezkuwichain.io (#21)

* docs: generate the API reference for developers.pezkuwichain.io

Add TypeDoc (0.28.20) and `yarn docs`, which builds the reference for the
nine public API packages from src/ into build-docs/, with a landing page
and a getting-started guide whose examples were run against the live
network. The PR workflow builds it so a broken doc comment or config is
caught before merge.

docs/ held only a redirect to polkadot.js.org; it now holds the guide
sources. The README, packages/api/README.md and three CHANGELOG entries
linked to js.pezkuwichain.app, a domain that is not ours and is listed
for sale; they now point to developers.pezkuwichain.io, the Pezkuwi
Portal, or the upstream polkadot.js.org pages the entries came from.

* ci(docs): deploy the reference to developers.pezkuwichain.io

On every master push that changes the generated reference, build it with
`yarn docs` and publish it to the web host the same way pezkuwi-apps
publishes the portal: an approved production environment holds the deploy
key, the bundle is unpacked into releases/<sha>, and going live is one
rename of the current symlink. The switch is checked through nginx for the
public name (deploy sha, index, main.js, search index) and rolled back if
the new release is not served. workflow_dispatch with rollback_to makes an
earlier release live again.

Release-bot version bumps ([CI Skip]) and changes that cannot affect the
output do not ask for an approval.

.github/workflows/docs-deploy.yml

@@ -0,0 +1,92 @@
+name: Docs
+on:
+  push:
+    branches:
+      - master
+    # Only what changes the generated reference. Every run asks for an approval,
+    # and an approval request that cannot matter teaches people to tap without
+    # reading.
+    paths:
+      - 'packages/**'
+      - 'docs/**'
+      - 'typedoc.config.mjs'
+      - 'yarn.lock'
+      - '.github/deploy/**'
+      - '.github/workflows/docs-deploy.yml'
+  workflow_dispatch:
+    inputs:
+      rollback_to:
+        description: 'Make an earlier release live again (full commit sha); empty = deploy this commit'
+        required: false
+        default: ''
+
+# Deploys wait for each other; a newer push queues behind a running one.
+concurrency:
+  group: deploy-docs
+  cancel-in-progress: false
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    # The release bot's version-bump commits change no source.
+    if: github.event.inputs.rollback_to == '' && !startsWith(github.event.head_commit.message, '[CI Skip]')
+    runs-on: ubuntu-latest
+    env:
+      YARN_ENABLE_SCRIPTS: false
+    steps:
+    - uses: actions/checkout@v4
+    - uses: actions/setup-node@v4
+      with:
+        node-version: 'lts/*'
+    - name: docs
+      run: |
+        yarn install --immutable
+        yarn docs
+        echo "$GITHUB_SHA" > build-docs/.deploy-sha
+        tar -C build-docs -czf docs-www.tgz .
+    - uses: actions/upload-artifact@v4
+      with:
+        name: docs-www
+        path: docs-www.tgz
+        retention-days: 7
+
+  # The only job that names the environment, so a run asks for approval once,
+  # and the deploy secrets (environment-scoped) exist only after it is given.
+  deploy:
+    needs: build
+    if: always() && (needs.build.result == 'success' || (needs.build.result == 'skipped' && github.event.inputs.rollback_to != ''))
+    runs-on: ubuntu-latest
+    environment: production
+    env:
+      HOST: ${{ secrets.DOCS_DEPLOY_HOST }}
+    steps:
+    - uses: actions/checkout@v4
+      with:
+        sparse-checkout: .github/deploy
+    - name: ssh setup
+      env:
+        KEY: ${{ secrets.DOCS_DEPLOY_SSH_KEY }}
+        KNOWN_HOSTS: ${{ secrets.DOCS_DEPLOY_KNOWN_HOSTS }}
+      run: |
+        install -m 700 -d ~/.ssh
+        printf '%s\n' "$KEY" > ~/.ssh/id_ed25519
+        chmod 600 ~/.ssh/id_ed25519
+        printf '%s\n' "$KNOWN_HOSTS" > ~/.ssh/known_hosts
+    - uses: actions/download-artifact@v4
+      if: github.event.inputs.rollback_to == ''
+      with:
+        name: docs-www
+    - name: upload
+      if: github.event.inputs.rollback_to == ''
+      run: scp -o BatchMode=yes docs-www.tgz "docs-deploy@$HOST:/var/www/docs-deploy/incoming/$GITHUB_SHA.tgz"
+    - name: go live
+      env:
+        ROLLBACK_TO: ${{ github.event.inputs.rollback_to }}
+      run: |
+        if [ -n "$ROLLBACK_TO" ]; then set -- rollback "$ROLLBACK_TO"; else set -- deploy "$GITHUB_SHA"; fi
+        # ssh hands its arguments to the remote shell as one string: only a
+        # bare sha may get there.
+        [[ $2 =~ ^[0-9a-f]{40}$ ]] || { echo "not a full commit sha: $2"; exit 1; }
+        ssh -o BatchMode=yes "docs-deploy@$HOST" bash -s -- "$@" < .github/deploy/release.sh