Configure GitHub Packages publishing

Scope the package as @richiesnitch/ads3-design-system, add repository +
publishConfig (GitHub Packages registry), and a publish-on-tag GitHub Actions
workflow. Add react/react-dom as devDependencies so the library build runs in
CI (they remain peerDependencies for consumers).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/publish-package.yml

@@ -0,0 +1,37 @@
+name: Publish package to GitHub Packages
+
+# Publishes @richiesnitch/ads3-design-system to GitHub Packages when a version
+# tag (v*) is pushed, or on manual dispatch. Uses the workflow's built-in
+# GITHUB_TOKEN (no PAT needed) — packages:write permission is granted below.
+on:
+  push:
+    tags:
+      - "v*"
+  workflow_dispatch:
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          registry-url: https://npm.pkg.github.com
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Build library
+        run: npm run build:lib
+
+      - name: Publish
+        run: npm publish
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.GITHUB_TOKEN }}