feat(release): Add prerelease validation to release planning

[bigtomcat6]

Summary

This PR updates the release pipeline for prerelease workflows and clarifies release versioning requirements. It adds prerelease input validation to release planning, tightens metadata checks for build/version inputs, and updates the release workflow documentation so prerelease behavior is explicit and discoverable.

How to test

• python3 .github/scripts/plan_release_test.py
• python3 .github/scripts/prepare_release_metadata_test.py
• python3 .github/scripts/release_policy_test.py
• Review .github/scripts/plan_release.py and related docs for updated prerelease validation and policy behavior.

Release impact

• Type: Added
• Release note:
  Adds prerelease support and input validation checks to the release planning pipeline, and updates release documentation to document prerelease and build version requirements.

Checklist

• I have seen this code, I have run this code, and I take responsibility for this code.
• PR title follows type(scope): Summary.
• Tests or a clear manual verification path are included.
• User-facing changes include release-note wording or Release impact: None.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[bigtomcat6]

reviewed