Gate the HF Space deploy on tests passing (item 5 from review)

deploy-to-hf.yml previously went straight from checkout to `git push
--force` on every push to main - no lint, no type-check, no test run in
between. Added a `test` job (install deps, install Playwright's Chromium,
run pytest) and made `deploy` depend on it via `needs: test`, so a commit
that breaks the test suite no longer reaches the production HF Space.

.github/workflows/deploy-to-hf.yml

@@ -7,7 +7,28 @@ on:
   workflow_dispatch:
 
 jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Install dependencies
+        run: pip install -r requirements-dev.txt
+
+      - name: Install Playwright's Chromium
+        run: playwright install --with-deps chromium
+
+      - name: Run tests
+        run: pytest
+
   deploy:
+    needs: test
     runs-on: ubuntu-latest
     steps:
       - name: Checkout