Implement transactional type-pack contract evolution

[callumalpass]

What changed

• Replaces the prerelease install-only type-pack path with first-class assess/apply APIs.
• Computes immutable canonical pack digests and writes exact portable lock provenance.
• Plans install, upgrade, downgrade, reconfigure, adoption, preservation, deletion, and conflict actions.
• Rechecks assessment digests inside the write transaction so stale plans cannot apply.
• Applies contract setup and managed resources atomically while preserving user divergence.
• Includes mdbase.lock.yaml in canonical collection snapshots.
• Adds command-layer integration and cross-version/conformance coverage.

Why

Contract changes previously left SDK consumers to infer collection state from failing operations. The engine now owns compatibility assessment and produces a deterministic migration plan that callers can explain before any write occurs.

Impact

This is intentionally breaking prerelease API work. The old install types/functions are removed in favor of structured assessment and application results.

Depends on mdbase-spec#44.

Validation

• full Rust workspace tests
• v0.3 conformance and migration fixtures
• runtime/integration tests
• package and snapshot regressions, including portable lock resources