feat(supervisor): expose sandbox name to middleware request context

[letv1nnn]

Summary

Adds the originating sandbox name to the supervisor middleware request context. Operator-run middleware already receives the sandbox ID; passing the name alongside it lets audit and approval interfaces show a human-readable identifier instead of an opaque UUID, using data the supervisor already owns.

Related Issue

Closes #2754

Changes

• Add sandbox_name field to RequestContext in proto/supervisor_middleware.proto; existing field numbers are unchanged for wire compatibility.
• Add sandbox_name to openshell_supervisor_middleware::HttpRequestInput and carry it into the gRPC RequestContext.
• Populate sandbox_id and sandbox_name from the process-wide openshell_ocsf::SandboxContext when the network supervisor builds middleware input.
• Inject the SandboxContext into middleware_request_input instead of reading the global inside it, making the identifier copy unit-testable with a real name.
• Document the request-context identifiers and their empty-string fallback in docs/extensibility/supervisor-middleware.mdx.
• Drop the #[cfg(target_os = "linux")] gate on the std::path::Path import in openshell-driver-podman's container.rs. Path is used unconditionally in a public function signature, so the gated import broke the non-Linux (macOS) build after merging main. Unrelated to the feature but required for the branch to compile cross-platform.

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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