[codex] Prepare Python SDK beta documentation and package metadata (#24836)

## Why

The initial public `openai-codex` beta should read and install like a
normal published Python package before a release tag is created. This
follows merged PR #24828, which establishes the independent SDK beta
release plumbing and exact runtime dependency.

## What changed

- Rewrote `sdk/python/README.md` as a compact PyPI-facing beta package
page: published installation, one quickstart, short login examples,
built-in help, and links to deeper guides.
- Updated the getting-started guide, API reference, FAQ, and examples
index to present the published beta consistently without repeating
onboarding in the package landing page or reference page.
- Made `pip install openai-codex` the primary install path while beta
releases are the only published SDK releases, with `--pre` documented
for opting into prereleases after a stable release exists.
- Added curated `help()` / `pydoc` docstrings across the public API and
generated public convenience methods through
`scripts/update_sdk_artifacts.py`.
- Declared the repository `Apache-2.0` license expression and
Documentation URL in package metadata, without introducing a duplicated
SDK-local license file.
- Kept the source distribution focused on installable package material
(`src/openai_codex`, `README.md`, and `pyproject.toml`); the repository
docs and runnable examples remain linked from the PyPI README.
- Built release artifacts in an Alpine container on the Ubuntu runner,
matching Python SDK CI and allowing type generation to install the
published `musllinux` runtime wheel.
- Added `twine check --strict` to the release workflow so malformed PyPI
metadata or rendered README content fails before publishing.
- Added focused SDK assertions for beta metadata, the exact runtime pin,
source distribution contents, and the built-in Python documentation
surface.

## Validation

- Ran `uv run --frozen --extra dev ruff check
scripts/update_sdk_artifacts.py src/openai_codex
tests/test_public_api_signatures.py
tests/test_artifact_workflow_and_binaries.py` before the final
README-only reductions and review-fix follow-ups.
- Built `openai_codex-0.1.0b1-py3-none-any.whl` and
`openai_codex-0.1.0b1.tar.gz` before the final README-only reductions
and review-fix follow-ups.
- Ran `python -m twine check --strict` on both built artifacts before
the final README-only reductions and review-fix follow-ups.
- Verified artifact metadata reports `Apache-2.0` without a duplicated
SDK-local license file.
- Verified `inspect.getdoc(...)` resolves documentation for the package,
`Codex`, `CodexConfig`, and key generated thread methods.
- Rebased the documentation/readiness change onto merged PR #24828
without changing the intended SDK or workflow file contents.
- Final verification is delegated to online CI for this PR.

.github/workflows/python-sdk-release.yml

@@ -28,9 +28,6 @@ jobs:
         with:
           python-version: "3.12"
 
-      - name: Install packaging tools
-        run: python -m pip install build uv==0.11.3
-
       - name: Validate tag and build Python SDK package
         shell: bash
         run: |
@@ -50,17 +47,33 @@ jobs:
             exit 1
           fi
 
-          cd sdk/python
-          uv sync --extra dev --frozen
-          uv run --extra dev --frozen python scripts/update_sdk_artifacts.py \
-            stage-sdk "${RUNNER_TEMP}/openai-codex" \
-            --sdk-version "${sdk_version}"
-
-          python -m build \
-            --wheel \
-            --sdist \
-            --outdir "${GITHUB_WORKSPACE}/dist/python-sdk" \
-            "${RUNNER_TEMP}/openai-codex"
+          # The pinned runtime currently publishes a musllinux Linux wheel.
+          # Build in Alpine so release type generation installs that wheel.
+          docker run --rm \
+            --user "$(id -u):$(id -g)" \
+            -e HOME=/tmp/codex-python-sdk-home \
+            -e UV_LINK_MODE=copy \
+            -e SDK_VERSION="${sdk_version}" \
+            -e SDK_STAGE_DIR="${RUNNER_TEMP}/openai-codex" \
+            -e SDK_DIST_DIR="${GITHUB_WORKSPACE}/dist/python-sdk" \
+            -v "${GITHUB_WORKSPACE}:${GITHUB_WORKSPACE}" \
+            -v "${RUNNER_TEMP}:${RUNNER_TEMP}" \
+            -w "${GITHUB_WORKSPACE}/sdk/python" \
+            python:3.12-alpine \
+            sh -euxc '
+              python -m venv /tmp/release-tools
+              /tmp/release-tools/bin/python -m pip install build twine uv==0.11.3
+              /tmp/release-tools/bin/uv sync --extra dev --frozen
+              /tmp/release-tools/bin/uv run --extra dev --frozen python scripts/update_sdk_artifacts.py \
+                stage-sdk "${SDK_STAGE_DIR}" \
+                --sdk-version "${SDK_VERSION}"
+              /tmp/release-tools/bin/python -m build \
+                --wheel \
+                --sdist \
+                --outdir "${SDK_DIST_DIR}" \
+                "${SDK_STAGE_DIR}"
+              /tmp/release-tools/bin/python -m twine check --strict "${SDK_DIST_DIR}/"*
+            '
 
       - name: Upload Python SDK package
         uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0