docs(config): list missing user-settable global keys in help

Summary

Fixes #8391 (closed).

The glab config Long help text (and the generated docs/source/config/_index.md) was a hardcoded bullet list that had drifted from KeySchema. git_protocol (as reported) plus branch_prefix, remote_alias, no_prompt, telemetry, notify_skill_updates, and the duo_cli_* / orbit_local_* auto-prompt keys were all missing.

This is a narrow drift fix. The long-term solution is #8375 (generate help/docs from KeySchema).

Test plan

• make check / lefthook run pre-push pass locally
• docs/source/config/_index.md regenerates cleanly with make gen-docs
• Reviewer spot-checks glab config -h output