fix(cache): restore large CARv2 blocks

[cre4ture]

Summary

• configure CARv2 reads to allow one section up to the Action's configured max-blob-size-mb, plus the fixed CID framing overhead
• add an end-to-end packed-cache regression test for a CAS object just over go-car's default 8 MiB section limit
• rebuild the v0.3.2 artifacts

Why

The first warm restore of IronMesh passed but consistently reported 11 fail-open misses while validating Action Results. The affected CAS blocks are larger than go-car's defensive 8 MiB default. IronMesh explicitly permits larger blobs (512 MiB by default), and CARv2 packs can contain a single large object, so the reader must use that configured limit.

Compatibility

This only changes the reader limit. Existing PACs remain immutable and become readable without reseeding.

Validation

• node --test action/*.test.js
• go test ./...
• go vet ./..., staticcheck, govulncheck, and actionlint
• packaged v0.3.2 binaries rebuilt twice byte-identically; checksums verified