Align validation Python runtime policy

[hdamker]

What type of PR is this?

cleanup
repository management

What this PR does / why we need it:

Aligns validation and release automation workflow runtimes on Python 3.14.

This PR:

• adds explicit PYTHON_VERSION: "3.14" workflow env pins where Python setup is owned by the workflow
• updates release automation shared actions to set up Python 3.14 directly
• renames validation Node runtime env usage from VALIDATION_NODE_VERSION to NODE_VERSION
• wires the release automation pre-snapshot validation Node setup through the same NODE_VERSION env
• updates runtime references in the reusable validation action docs and regression runner README

Which issue(s) this PR fixes:

Fixes #342

Special notes for reviewers:

The reusable validation and release automation workflows are consumed by API repositories, so this intentionally changes the downstream Python runtime from 3.11 to 3.14.

Local validation:

• python3 -m pytest tooling_lib/tests
• touched workflow/action YAML parsed successfully
• actionlint passed with the existing create-github-app-token metadata and shellcheck baseline categories ignored

Changelog input

release-note
Align validation and release automation workflow runtime pins to Python 3.14.

Additional documentation

This section can be blank.

docs
No additional documentation.

[Kevsy]

LGTM

[rartych]

LGTM