feat(release): add versioned SN39 seals

[wallscaler]

What changed

• preserve the historical root release.json seal
• publish later seals under digest-addressed releases/sha256/<digest>.json[.sig] paths
• add an operation-bound, filesystem-read-only preflight mode
• bind the rotating controlled-evidence selector to one safe direct-sibling epoch by directory descriptor
• verify digest-addressed releases in the public reproducer
• provision versioned release directories and document the operator flow
• add adversarial tests for symlink escape, publication conflict, historical preservation, context separation, and Git-index immutability

Why

The current root seal is publish-once. A second ceremony needs a new immutable generation without replacing historical bytes. The previous finalizer also rejected the live current selector symlink, and an ordinary git status could refresh .git/index during a claimed read-only preflight.

Impact

This prepares a legitimate second-generation SN39 ceremony. It does not authorize or perform a seal, chain write, deployment, or production mutation. Operators still need matching immutable producer and validator revisions, current passing provenance gates, and complete release pins before preflight.

Validation

• independent security review after remediation: PASS
• release-generation tests: 20 passed
• expanded release, reproduction, manifest, and launcher set: 80 passed
• Ruff check: passed
• Ruff format check: passed
• git diff --check: passed
• live read-only route audit: nested evidence paths are supported; actual versioned artifact retrieval remains unproven until a legitimate publication exists

Known boundary

The full repository suite is not proven in the local macOS environment because unrelated installed dependency conflicts and /usr/bin/python3.12 fixture assumptions prevent complete collection. GitHub CI remains required before merge.

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