chore: release 0.12.20

[danielgwilson]

Summary

• bump mimetic-cli from 0.12.19 to 0.12.20
• update the release metadata test to the new version

Public Boundary

• This change does not include PII, PHI, secrets, keys, tokens, raw private transcripts, private screenshots, or private customer/patient data.
• Examples, fixtures, personas, screenshots, and artifact snippets are synthetic or redacted.
• Product-specific private context stays outside this repository or in synthetic adapter fixtures only.

Proof

• pnpm release:check — passed
• git diff --check — passed

Remaining Gaps

• After this PR merges, tag the merged main commit as v0.12.20 and let .github/workflows/publish.yml publish through trusted publishing.