Add GitHub Packages publish workflow

- Alternative to npm public registry while waiting for npm org access
- Uses GITHUB_TOKEN (automatic, no secret setup needed)
- Supports same version bump and tagging features as npm workflow

Install from GitHub Packages:
npm install @nhsdigital/fdp-design-system --registry=https://npm.pkg.github.com

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: fergusbisset

.github/workflows/github-packages-publish.yml

@@ -0,0 +1,89 @@
+name: Publish to GitHub Packages
+
+on:
+  release:
+    types: [published]
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Optional semver bump to apply before publishing (patch, minor, major, prerelease)'
+        required: false
+        type: string
+      preid:
+        description: 'Prerelease identifier when version is prerelease (e.g., alpha, beta, rc)'
+        required: false
+        type: string
+      tag:
+        description: 'NPM dist-tag to publish under (e.g., latest, alpha, beta, next)'
+        required: false
+        default: 'latest'
+        type: string
+
+permissions:
+  contents: write
+  packages: write
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node for GitHub Packages
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          registry-url: 'https://npm.pkg.github.com'
+          scope: '@nhsdigital'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Optionally bump version (manual dispatch only)
+        if: ${{ github.event_name == 'workflow_dispatch' && inputs.version != '' }}
+        run: |
+          git config user.name github-actions
+          git config user.email [email protected]
+          if [ "${{ inputs.version }}" = "prerelease" ]; then
+            npm version prerelease --preid=${{ inputs.preid || 'alpha' }} -m "chore(release): %s"
+          else
+            npm version ${{ inputs.version }} -m "chore(release): %s"
+          fi
+
+      - name: Run tests
+        run: |
+          npm run lint
+          npm run test:components
+          npm run test:ssr-components
+
+      - name: Build
+        run: npm run build
+
+      - name: Publish to GitHub Packages
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          if [ -n "${{ inputs.tag }}" ] && [ "${{ inputs.tag }}" != "latest" ]; then
+            npm publish --registry=https://npm.pkg.github.com --tag ${{ inputs.tag }}
+          else
+            npm publish --registry=https://npm.pkg.github.com
+          fi
+
+      - name: Push version bump (when version bumped)
+        if: ${{ github.event_name == 'workflow_dispatch' && inputs.version != '' }}
+        run: |
+          VERSION=$(node -p "require('./package.json').version")
+          git push origin HEAD
+          git tag v$VERSION
+          git push origin v$VERSION
+
+      - name: Summary
+        run: |
+          VERSION=$(node -p "require('./package.json').version")
+          echo "Published @nhsdigital/fdp-design-system@$VERSION to GitHub Packages" >> $GITHUB_STEP_SUMMARY
+          echo "" >> $GITHUB_STEP_SUMMARY
+          echo "Install with:" >> $GITHUB_STEP_SUMMARY
+          echo "\`\`\`" >> $GITHUB_STEP_SUMMARY
+          echo "npm install @nhsdigital/fdp-design-system --registry=https://npm.pkg.github.com" >> $GITHUB_STEP_SUMMARY
+          echo "\`\`\`" >> $GITHUB_STEP_SUMMARY