S9: management commands — drivers, connectors, doc, help, version, completion #13

Part of #17. Design: docs/design.md §3.

Scope

The management commands:

• relix drivers ls|install NAME and relix connectors ls|install NAME replace the run-time --download-drivers/--download-connectors flags.
• relix doc [TOPIC] shows reference pages from DocRegistry. On a terminal it goes through $PAGER.
• relix help [COMMAND] shows command usage.
• relix version shows the front-end and engine versions.
• relix completion bash|zsh|fish|powershell prints a completion script.

ls output uses the S2 renderers.

Dependencies

• S1 (S1: command skeleton — script sources, exit codes, diagnostics, profiles, engine options #4), S2 (S2: output — isatty defaults, last-query rule, assertions, EPIPE/SIGINT discipline #6).

Acceptance

• Each command end-to-end.
• doc resolves every key the reference-page index in relix-console holds.
• Each completion script is syntax-checked by its shell where that shell is available in CI.