python-sdk: generated type foundation (all v2 schemas) (#13953)

## Summary
Foundation PR only (base for PR #3).

This PR contains the SDK runtime foundation and generated artifacts:

- pinned runtime binary in `sdk/python/bin/` (`codex` or `codex.exe` by
platform)
- single maintenance script:
`sdk/python/scripts/update_sdk_artifacts.py`
- generated protocol/types artifacts under:
  - `sdk/python/src/codex_app_server/generated/protocol_types.py`
  - `sdk/python/src/codex_app_server/generated/schema_types.py`
  - `sdk/python/src/codex_app_server/generated/v2_all/*`
- generation-contract test wiring (`tests/test_contract_generation.py`)

## Release asset behavior
`update_sdk_artifacts.py` now:
- selects latest release by channel (`--channel stable|alpha`)
- resolves the correct asset for current OS/arch
- extracts platform binary (`codex` on macOS/Linux, `codex.exe` on
Windows)
- keeps runtime on single pinned binary source in `sdk/python/bin/`

## Scope boundary
- ✅ PR #2 = binary + generation pipeline + generated types foundation
- ❌ PR #2 does **not** include examples/integration logic polish (that
is PR #3)

## Validation
- Ran: `python scripts/update_sdk_artifacts.py --channel stable`
- Regenerated and committed resulting generated artifacts
- Local tests pass on branch

sdk/python/pyproject.toml

@@ -0,0 +1,63 @@
+[build-system]
+requires = ["hatchling>=1.24.0"]
+build-backend = "hatchling.build"
+
+[project]
+name = "codex-app-server-sdk"
+version = "0.2.0"
+description = "Python SDK for Codex app-server v2"
+readme = "README.md"
+requires-python = ">=3.10"
+license = { text = "Apache-2.0" }
+authors = [{ name = "OpenClaw Assistant" }]
+keywords = ["codex", "json-rpc", "sdk", "llm", "app-server"]
+classifiers = [
+  "Development Status :: 4 - Beta",
+  "Intended Audience :: Developers",
+  "License :: OSI Approved :: Apache Software License",
+  "Programming Language :: Python :: 3",
+  "Programming Language :: Python :: 3.10",
+  "Programming Language :: Python :: 3.11",
+  "Programming Language :: Python :: 3.12",
+  "Programming Language :: Python :: 3.13",
+  "Topic :: Software Development :: Libraries :: Python Modules",
+]
+dependencies = ["pydantic>=2.12"]
+
+[project.urls]
+Homepage = "https://github.com/openai/codex"
+Repository = "https://github.com/openai/codex"
+Issues = "https://github.com/openai/codex/issues"
+
+[project.optional-dependencies]
+dev = ["pytest>=8.0", "datamodel-code-generator==0.31.2"]
+
+[tool.hatch.build]
+exclude = [
+  ".venv/**",
+  ".venv2/**",
+  ".pytest_cache/**",
+  "dist/**",
+  "build/**",
+]
+
+[tool.hatch.build.targets.wheel]
+packages = ["src/codex_app_server"]
+include = [
+  "src/codex_app_server/bin/**",
+  "src/codex_app_server/py.typed",
+]
+
+[tool.hatch.build.targets.sdist]
+include = [
+  "src/codex_app_server/**",
+  "README.md",
+  "CHANGELOG.md",
+  "CONTRIBUTING.md",
+  "RELEASE_CHECKLIST.md",
+  "pyproject.toml",
+]
+
+[tool.pytest.ini_options]
+addopts = "-q"
+testpaths = ["tests"]