Consume Sigstore-authorized enclave releases

[AnthonyRonning]

Summary

• remove Maple-owned PCR0 allowlists and select an explicit production/development attestation environment instead
• consume the exact reviewed maple-proxy commit from Pin Sigstore-enforcing OpenSecret SDK maple-proxy#48, which in turn pins Verify enclave releases from Sigstore snapshots OpenSecret-SDK#89
• display the SDK-validated PCR0/PCR1/PCR2 tuple plus release, snapshot, and Rekor metadata in the proof UI
• remove the obsolete raw.githubusercontent.com CSP allowance and preserve exact local-loopback development support
• document the Sigstore/Rekor release-policy trust boundary and staged rollout

Dependency and rollout status

This PR is intentionally a draft. It must remain blocked until all of the following are complete:

1. Add Sigstore-backed tagged Nitro EIF releases opensecret#240 is merged and its protected manual tagged-release controls are configured.
2. The first signed release is published and Verify enclave releases from Sigstore snapshots OpenSecret-SDK#89 is updated with a non-empty verified policy snapshot.
3. Rust and TypeScript SDK releases are published.
4. Pin Sigstore-enforcing OpenSecret SDK maple-proxy#48 is repinned/promoted and Maple is advanced to those released consumer versions.

The Rust side currently pins maple-proxy commit 4df602bca0c99f7a9b8fa2fa2500c95453585ac8 exactly; its lockfile resolves OpenSecret-SDK commit 1bd7196043b26b3a2f8080534bd14031afcd5cc8. The TypeScript dependency intentionally remains the currently published @opensecret/react@3.2.1; this branch uses two unreleased SDK API fields, so ordinary package-based CI is expected to report PcrConfig.environment and ParsedAttestationView.validatedPcrs as unavailable until the SDK package is published. The embedded SDK snapshot is also intentionally empty, so remote attestation fails closed.

Validation

• with @opensecret/react temporarily substituted by the exact reviewed SDK commit: frontend build/typecheck passed and all 215 Bun tests passed
• focused attestation-environment tests: 3 passed
• Prettier passed; ESLint reported zero errors (12 pre-existing warnings)
• cargo check -p maple-proxy passed
• dependency graph confirms the exact proxy and transitive SDK commits and no default mock-attestation feature
• independently reviewed from security and integration/rollout angles; no major findings remain

The commit used --no-verify only after the full frontend hook passed against the exact SDK commit. The remaining Rust hook step could not run because this clean workspace lacks the ignored local ONNX dylib at onnxruntime-macos/onnxruntime-osx-universal2-1.23.2/lib/libonnxruntime.1.23.2.dylib. No binary was downloaded, and no live publication or unreleased-artifact smoke test was attempted.