#710 chore(runner): pin versions.toml to 2.337.0 [skip ci]

Summary

• Bump runner_version in versions.toml and experiments/mitm/versions.toml to 2.337.0.
• Update protocol-target docs to match.
• Leave green-gate benchmarks/conformance/targets.toml on flat v2.336.0 until nested v2.337.0 captures are gate-ready.
• Fix stale compatibility limitation: local-composite nested remotes are admitted now.

Test plan

• Commit messages include [skip ci]
• Confirm Mintlify/docs sync picks up docs/compatibility.mdx after merge

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Summary by cubic

Bumps the pinned actions/runner compatibility target from v2.336.0 to v2.337.0 across versions.toml, experiments/mitm/versions.toml, and the protocol/compatibility docs, and fixes a stale compatibility limitation for local-composite nested remotes.

• Keeps the green-gate replay list in benchmarks/conformance/targets.toml on the flat v2.336.0 corpus until the v2.337.0 captures have protocol-equivalent provenance.
• Docs fixes
  • Replaces the outdated "remote actions inside local composites" limitation with the current behavior: local-composite nested remotes are admitted, and only undeclared remotes or unreadable manifests return 403.
  • Updates the upstream reference commit and previous baseline in fidelity-gap.md.