chore: add unit tests for pure functions + CI test job

- Unit tests for normalize_email_address, payload_matches_participant,
  format_search_result (9 test cases across 3 test classes)
- New 'test' job in CI workflow (runs before build)
- pytest.ini for pythonpath config

.gitea/workflows/docker-build.yaml

@@ -9,11 +9,24 @@ on:
     - cron: '0 0 * * *'
 
 jobs:
-  build:
+  test:
     runs-on: ubuntu-latest
     steps:
-      - name: Checkout
-        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
+      - uses: actions/setup-python@v6
+        with:
+          python-version: "3.13"
+      - name: Install dependencies
+        run: |
+          pip install -r requirements.txt pytest
+      - name: Run unit tests
+        run: pytest tests/ -v
+
+  build:
+    runs-on: ubuntu-latest
+    needs: test
+    steps:
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@d7f5e7f509e45cec5c76c4d5afdd7de93d0b3df5 # v4