chore: upgrade Python version to 3.13

- Update requires-python to >=3.13 in pyproject.toml
- Update ruff and black target versions to py313
- Update Dockerfile to use python:3.13-alpine
- Add explicit Python 3.13 setup in CI workflow
- Regenerate uv.lock for Python 3.13

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -15,6 +15,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - name: Set up Python 3.13
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
       - uses: astral-sh/setup-uv@v4
         with:
           version: "latest"