The tag validator required a leading `v`, so dispatching create-release
with `1.84.0` (or `1.84.0rc1`, `1.84.0.dev42`, `1.84.0.post1`) failed
even though those are the new naming convention. Make the leading `v`
optional in both create-release.yml and create-release-branch.yml so
both legacy (`v1.83.10-stable`, `v1.83.14.rc.1`, `v1.82.3.dev.9`,
`v1.82.3-stable.patch.4`, `v1.83.13-nightly`) and new PEP 440 forms are
accepted during the transition. Refresh the input descriptions to show
the new examples.
Extracts release branch creation into a separate reusable workflow
(create-release-branch.yml) that can be triggered independently via
workflow_dispatch or called from other workflows via workflow_call.
create-release.yml now dispatches it as a dependent job after the
release publishes, keeping both workflows decoupled.