[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.

sdk/python/docs/faq.md

@@ -1,5 +1,18 @@
 # FAQ
 
+## Is the Python SDK stable?
+
+`openai-codex` is a public beta. Install it with
+`pip install openai-codex`; public APIs may change before `1.0`. While beta
+releases are the only published SDK releases, pip selects the latest beta.
+After a stable release exists, pass `--pre` to opt into newer prereleases.
+
+## Why does the SDK install a runtime package?
+
+The SDK and runtime packages are versioned independently. Each SDK release
+pins one compatible runtime dependency, so `openai-codex==0.1.0b1` installs
+`openai-codex-cli-bin==0.132.0` automatically.
+
 ## Thread vs turn
 
 - A `Thread` is conversation state.
@@ -84,9 +97,9 @@ This avoids duplicate ways to do the same operation and keeps behavior explicit.
 
 Common causes:
 
-- published runtime package (`openai-codex-cli-bin`) is not installed
+- installation is incomplete and the pinned `openai-codex-cli-bin` dependency is missing
 - local `codex_bin` override points to a missing file
-- installed Codex runtime version older than the SDK schema
+- a custom local Codex executable does not support the SDK operation being used
 
 ## Why does a turn "hang"?
 
@@ -99,7 +112,8 @@ A turn is complete only when `turn/completed` arrives for that turn ID.
 
 Use `retry_on_overload(...)` for transient overload failures (`ServerBusyError`).
 
-Do not blindly retry all errors. For `InvalidParamsError` or `MethodNotFoundError`, fix inputs or update the runtime/schema version instead.
+Do not blindly retry all errors. For `InvalidParamsError` or
+`MethodNotFoundError`, fix the input or use the runtime pinned by the SDK.
 
 ## Common pitfalls