docs: close Slice P release journal

[gnanirahulnutakki]

Summary

• mark the Slice P GSTACK journal as shipped
• record the public v0.1.0, release/main promotion, and immutable-release control
• anchor final CI, CodeQL, consumer verification, and zero-alert evidence
• keep E9 E9: Deployment and packaging #27 open for the remaining hub packaging features

Validation

• git diff --check
• README reviewed; no change needed because the Homebrew trust/install path is already documented
• source/runtime content is unchanged; full CI and CodeQL are expected to remain green

Refs #27.