refactor(attestation): isolate Cocos and hardware modules

[thinksyncs]

Summary

• Integrate the v2 module-path migration from PR chore(module): migrate repository identity to v2 #29.
• Keep the ASB core platform-neutral and move Cocos-specific composition outside the root module.
• Isolate direct AMD SEV-SNP and Intel TDX support behind nested Go module boundaries.

Changes

• Replace root-level hardware verifier construction with injected evidence and policy interfaces.
• Move the Cocos adapter, platform selection, agent, CLI, and hardware runner to integrations/cocos.
• Harden signed EAT, CoRIM, legacy SNP, and TDX appraisal compatibility paths.
• Add root, nested-module, and tag-oriented release gates with GOWORK=off checks.
• Pin Go workflows to Go 1.26.6 and document the v2 migration and release sequence.

Testing

• make check-attestation-release
• make -C integrations/cocos test
• GOWORK=off go mod tidy -diff, go test -race ./..., and go vet ./... in both SNP and TDX modules
• actionlint on all changed workflows
• shellcheck and sh -n on the new release scripts
• git diff --check and gofmt verification for changed Go files

Notes

• No SNP, TDX, or TPM hardware qualification has been performed on this branch.
• The Cocos integration and hardware modules remain experimental and do not carry a production-readiness claim.
• TDX strict-collateral success still needs a live positive fixture.
• Nested module tags, dependency cleanup, the root release candidate tag, and the prerelease are intentionally deferred until this PR is merged and CI is green.