fix(release): prepare v2.0.0-rc.2

[ryan-wong-coder]

Summary

• prepare the corrected v2.0.0-rc.2 release metadata without mutating RC.1
• update README, integrations, and six-language website onboarding to consume RC.2 artifacts
• resolve the immutable OCI digest from the published container evidence instead of hardcoding a pre-release digest
• record deterministic cross-platform release verification and unchanged V2/V5 compatibility boundaries

Validation

• go mod tidy -diff
• go test -count=1 -mod=readonly ./...
• go test -race -count=1 -mod=readonly ./internal/supplychain ./cmd/trustdb
• go mod verify
• go run ./cmd/trustdb release verify-policy --root . --policy supply-chain/production-inputs.json
• npm --prefix website ci
• npm --prefix website run build
• replayed the published RC.1 container-digest JSON through the new POSIX digest resolver

Refs #612