CLI reachability SSOT

The top-level reachability matrix (| \build` | …) is authored in **[reference/cli.md](../reference/cli.md)** under **CLI command reachability** (content merged from the former cli-reachability.md`).

When you add a vox-cli registry entry with reachability_required: true, extend that table in reference/cli.md and run vox ci command-compliance.

This architecture page exists so doc-inventory / SSOT file lists keep a stable anchor; it is not a second copy of the table.