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

README.md

@@ -12,6 +12,7 @@ This repository is a monorepo for the Kaya framework. The code is split into ind
 - **kaya-session-redis** — Redis-backed session storage (`packages/kaya-session-redis/`)
 - **kaya-session-memcache** — memcached-backed session storage (`packages/kaya-session-memcache/`)
 - **kaya-oidc** — OpenID Connect authentication (`packages/kaya-oidc/`)
+- **kaya-openapi** — automatic OpenAPI specification generation (`packages/kaya-openapi/`)
 
 Additional `kaya-*` packages can be added as new directories under `packages/`.
 
@@ -26,7 +27,7 @@ pip install --index-url https://gitea.woggioni.net/api/packages/woggioni/pypi/si
 Install the packages in development mode:
 
 ```bash
-pip install -e packages/kaya-core -e packages/kaya-rsgi -e packages/kaya-session -e packages/kaya-session-redis -e packages/kaya-session-memcache -e packages/kaya-oidc
+pip install -e packages/kaya-core -e packages/kaya-rsgi -e packages/kaya-session -e packages/kaya-session-redis -e packages/kaya-session-memcache -e packages/kaya-oidc -e packages/kaya-openapi
 ```
 
 Run the example:
@@ -44,6 +45,7 @@ python -m unittest discover -s packages/kaya-session/tests
 python -m unittest discover -s packages/kaya-session-redis/tests
 python -m unittest discover -s packages/kaya-session-memcache/tests
 python -m unittest discover -s packages/kaya-oidc/tests
+python -m unittest discover -s packages/kaya-openapi/tests
 ```
 
 ## Static analysis
@@ -55,6 +57,7 @@ mypy -p kaya.session
 mypy -p kaya.session.redis
 mypy -p kaya.session.memcache
 mypy -p kaya.oidc
+mypy -p kaya.openapi
 ```
 
 ## Building packages
@@ -66,4 +69,5 @@ python -m build packages/kaya-session
 python -m build packages/kaya-session-redis
 python -m build packages/kaya-session-memcache
 python -m build packages/kaya-oidc
+python -m build packages/kaya-openapi
 ```