Publish prerelease packages and enforce a consumer sample gate

[LeftTwixWand]

Outcome

Validate versioned prerelease packages through an independent consumer pattern before compatibility changes are accepted.

Acceptance criteria

• Publish versioned prerelease packages.
• Restore them in a generically named external consumer sample.
• Exercise the sample in CI.
• Fail compatibility checks when the public consumer pattern breaks.

Non-goals

• Treating repository-internal compilation as sufficient compatibility evidence.