docs(rfc): add loose inspection contract proposal

[afourniernv]

Summary

Adds RFC 0006 as a narrower alternative to RFC 0005 for OpenShell and NeMo Relay interoperability around outbound inspection.

Related Issue

References NVIDIA/NeMo-Relay#277 and #1738

Changes

• Add rfc/0006-loose-inspection-contract/README.md
• Define an OpenShell-owned runtime enforcement seam rather than an OpenShell-owned general middleware subsystem
• Document the intended boundary between OpenShell, NeMo Relay, and the platform or harness layer

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)

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[drew]

@alexclewontin lets start with a feature request issue instead of a RFC. We can open an RFC if it requires further design.

I would also alternatively suggest contributing to the discussion in #1738. That RFC is intended to enable things like NeMo Relay. If NeMo-Relay integration isn't enabled through the middleware, we may want to adjust that design instead of creating new one.

cc @pimlock @kirit93.