[codex] Stage Python SDK beta versions from release tags (#24872)

## Summary
- Treat `sdk/python` as a development template with source version
`0.0.0-dev`, matching the existing Python runtime packaging pattern.
- Have `python-v*` tags supply the published SDK beta version through
the existing `stage-sdk --sdk-version` path.
- Remove the workflow check requiring a source version bump for each
beta release and remove its now-unused host Python setup step.
- Keep the reviewed runtime dependency pin at
`openai-codex-cli-bin==0.132.0`.
- Remove beta-number-specific documentation so it does not need editing
for each publish.

## Why
The package staging script already writes the release version into the
artifact. Requiring the checked-in SDK template version to match every
tag adds release-only source churn without changing the package users
receive.

## Validation
- Not run locally; relying on online CI for this workflow and metadata
change.

## Release
After this PR lands, publish the next beta by pushing tag
`python-v0.1.0b2` from merged `main`.

sdk/python/tests/test_artifact_workflow_and_binaries.py

@@ -239,17 +239,17 @@ def test_runtime_distribution_name_is_consistent() -> None:
     )
 
 
-def test_source_sdk_package_pins_published_runtime() -> None:
-    """The source package metadata should pin the runtime wheel that ships schemas."""
+def test_source_sdk_template_pins_published_runtime() -> None:
+    """The source template should carry a development version and reviewed runtime pin."""
     script = _load_update_script_module()
     pyproject = tomllib.loads((ROOT / "pyproject.toml").read_text())
 
     assert {
-        "sdk_version": pyproject["project"]["version"],
+        "sdk_template_version": pyproject["project"]["version"],
         "runtime_pin": script.pinned_runtime_version(),
         "dependencies": pyproject["project"]["dependencies"],
     } == {
-        "sdk_version": "0.1.0b1",
+        "sdk_template_version": "0.0.0-dev",
         "runtime_pin": "0.132.0",
         "dependencies": [
             "pydantic>=2.12",
@@ -319,7 +319,7 @@ def test_runtime_setup_reads_independent_runtime_pin_and_release_tags() -> None:
 
     assert {
         "package_name": runtime_setup.PACKAGE_NAME,
-        "sdk_version": pyproject["project"]["version"],
+        "sdk_template_version": pyproject["project"]["version"],
         "runtime_pin": runtime_setup.pinned_runtime_version(),
         "normalized_release_version": runtime_setup._normalized_package_version(
             "rust-v0.116.0-alpha.1"
@@ -327,7 +327,7 @@ def test_runtime_setup_reads_independent_runtime_pin_and_release_tags() -> None:
         "release_tag": runtime_setup._release_tag("0.116.0a1"),
     } == {
         "package_name": "openai-codex-cli-bin",
-        "sdk_version": "0.1.0b1",
+        "sdk_template_version": "0.0.0-dev",
         "runtime_pin": "0.132.0",
         "normalized_release_version": "0.116.0a1",
         "release_tag": "rust-v0.116.0-alpha.1",