Retire central prerelease lifecycle workflows

[rmcdaniel]

Summary

• remove 16 beta/RC launch, release-plan, recovery, and issue-lifecycle workflows that no longer have post-stable authority
• replace the authority README and release guidance with the direct GitHub/repository-owned model
• retain only the still-consumed release-recovery conformance and Rust visual workflows plus one small repository test workflow
• rename the retained visual capture entry point and schema away from pipeline terminology

This is the first landing for #115. Static contracts that current downstream repositories still read remain in place until their component recovery consumers and stale prerelease version authority are removed.

Validation

• 53 retained Python contract tests
• 75 browser capture checks
• actionlint
• git diff --check

[rmcdaniel]

Branch protection now requires the replacement Shared contract tests GitHub Actions check from this PR instead of the deleted Control-plane source qualification job. The replacement check passed on run 33471646077. No protection was removed; the required check was renamed to the retained repository test surface.