[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/uv.lock

@@ -282,7 +282,7 @@ wheels = [
 
 [[package]]
 name = "openai-codex"
-version = "0.1.0b1"
+version = "0.0.0.dev0"
 source = { editable = "." }
 dependencies = [
     { name = "openai-codex-cli-bin" },