release: attach proxy artifacts to Maple releases

[AnthonyRonning]

Summary

• build native maple-proxy archives for Linux x86_64, Linux ARM64, Apple Silicon macOS, and Windows x86_64 during every Maple release
• attest, checksum, upload, and re-download those assets on the existing Maple GitHub Release
• preserve the one-release invariant: no proxy Release, no proxy tag, and no dependency from latest.json publication onto proxy jobs
• document stable releases/latest/download URLs and extend the release verifier and release skill

Stack

• Base: build: use in-tree proxy and Rust SDK #854
• Merge only after Import maple-proxy into proxy/ with history #851, ci: integrate proxy checks into Maple #853, and build: use in-tree proxy and Rust SDK #854 land in order

Validation

• built and ran the macOS ARM64 release archive locally; maple-proxy --version reported 0.3.3
• 27 proxy tests passed; strict Clippy and formatting passed
• release topology tests: 25 passed
• proxy artifact fixtures cover complete, missing, tampered, extra-member, and unexpected-archive cases
• actionlint passed
• Nix release-gates build passed
• Nix flake evaluation passed for all systems

The remaining three native archives are intentionally validated by their matching GitHub-hosted runners in CI.

[cloudflare-workers-and-pages]

Deploying maple with    Cloudflare Pages

Latest commit:	7e4da93
Status:	✅  Deploy successful!
Preview URL:	https://16424f56.maple-ca8.pages.dev
Branch Preview URL:	https://codex-proxy-release-artifact.maple-ca8.pages.dev

View logs