Add a browser playground that runs groundcheck through Pyodide

.github/workflows/pages.yml

@@ -0,0 +1,38 @@
+name: pages
+
+on:
+  push:
+    branches: [main]
+    paths: ["groundcheck/**", "site/**", ".github/workflows/pages.yml"]
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: true
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - uses: actions/checkout@v7
+      # The playground runs the package itself in the browser, so it ships the
+      # same source the command line does.
+      - name: Assemble the site
+        run: |
+          mkdir _site
+          cp site/* _site/
+          zip -qr _site/groundcheck.zip groundcheck -x '*/__pycache__/*'
+      - uses: actions/configure-pages@v6
+      - uses: actions/upload-pages-artifact@v5
+        with:
+          path: _site
+      - id: deployment
+        uses: actions/deploy-pages@v5

README.md

@@ -9,6 +9,10 @@ A **deterministic groundedness linter** for RAG and LLM answers. It reads an
 answer and the sources it was supposed to be based on, and flags the claims that
 aren't actually supported — above all, **fabricated numbers**.
 
+**[Try it in your browser](https://rootx22.github.io/groundcheck/)**: paste an
+answer and its sources and see what it flags. It runs groundcheck itself through
+Pyodide, so nothing you paste leaves the page and no model is called.
+
 ```console
 $ groundcheck --answer answer.txt --source q3-report.txt --fail-on high