Add kaya-openapi package for automatic OpenAPI spec generation

- New packages/kaya-openapi with OpenAPIMixin, @operation decorator,
  and generate_spec() that walks the routing tree
- Enables kaya-core's Tree.register to expose the original handler
  callback as an instance attribute for metadata introspection
- Registers GET /openapi.json and GET /docs (Swagger UI) routes
- Supports  and  path parameters, docstring
  descriptions, @operation metadata, and excludes wildcard/WS routes
- Adds example/openapi.py, updates CI, README, and requirements

.gitea/workflows/build.yaml

@@ -48,6 +48,10 @@ jobs:
         run: |
           .venv/bin/python -m mypy -p kaya.oidc
           .venv/bin/python -m unittest discover -s packages/kaya-oidc/tests
+      - name: Check kaya-openapi
+        run: |
+          .venv/bin/python -m mypy -p kaya.openapi
+          .venv/bin/python -m unittest discover -s packages/kaya-openapi/tests
       - name: Publish kaya-core artifacts
         env:
           TWINE_REPOSITORY_URL: ${{ vars.PYPI_REGISTRY_URL }}
@@ -96,3 +100,11 @@ jobs:
         run: |
           .venv/bin/pyproject-build packages/kaya-oidc
           .venv/bin/twine upload --repository gitea packages/kaya-oidc/dist/*.whl packages/kaya-oidc/dist/*.tar.gz
+      - name: Publish kaya-openapi artifacts
+        env:
+          TWINE_REPOSITORY_URL: ${{ vars.PYPI_REGISTRY_URL }}
+          TWINE_USERNAME: ${{ vars.PUBLISHER_USERNAME }}
+          TWINE_PASSWORD: ${{ secrets.PUBLISHER_TOKEN }}
+        run: |
+          .venv/bin/pyproject-build packages/kaya-openapi
+          .venv/bin/twine upload --repository gitea packages/kaya-openapi/dist/*.whl packages/kaya-openapi/dist/*.tar.gz