Accept supported ReScript 13 prereleases and verify tarball installation #384

Part of #382 — v1.0.0 alpha readiness.

Problem

package.json:55-L60 declares the compiler peer as >=13, while the lockfile uses 13.0.0-alpha.5. SemVer excludes that prerelease from the peer range. ReScript 13 being in alpha is intentional and is not itself a release blocker.

Review reproduction using the actual npm pack artifact:

• Fresh installation fails with ETARGET: No matching version found for rescript@>=13.
• Installation with explicit rescript@13.0.0-alpha.5 fails with ERESOLVE.
• Manually linking that compiler allows compilation, but is not an installation pass.

The existing consumer checks copy sources and symlink the compiler rather than installing the package: scripts/check-features.mjs:263-L292.

Acceptance criteria

• Select and document the supported/tested ReScript 13 alpha version(s); use a peer range that explicitly admits them.
• Keep the development compiler, lockfile, and stated minimum compatibility consistent. Do not silently claim compatibility with untested earlier versions.
• A fresh temporary project can install the packed tarball and a supported compiler without --force, --legacy-peer-deps, manual links, or copied package sources.
• The installed artifact compiles representative default, Fetch-only, and SafeFetch consumers, with a Node-safe runtime smoke test.
• Preserve the intended rejection of SafeFetch when only the Fetch feature is enabled.
• CI/release checks validate tarball contents, including source/interfaces/config/license, and exclude tests, tooling, and build output.
• Unsupported compiler versions fail with useful package-manager diagnostics.

Validation

Run the existing build/feature/test/format checks plus the new clean tarball-install test on the documented CI toolchain. A successful repository build alone does not close this issue.

Related validation work: #383. This issue owns installation and execution from the npm artifact; that issue owns the general runtime-test categories and browser harness.