fix(docs): isolate command inventory helpers

[John-David Dalton (jdalton)]

Note

Low Risk
Repo-internal docs/check scripts and tests only; behavior changes are limited to stricter AST parsing and snapshot alignment for config help text.

Overview
Refactors CLI command documentation tooling by moving inventory extraction (inventory.mts, custom-routes.mts, shared util.mts) out of scripts/repo/check/ into scripts/repo/docs/commands/, and renaming the coverage gate to docs-commands-are-complete.mts with updated docs:commands:* npm scripts and unit test paths.

The shared AST helpers gain an explicit AstNode shape and safer property access (e.g. arguments on call expressions), with small hardening in the markdown checker (table header guards, SCRIPT_META.json: 'result'). An integration snapshot for socket config auto help now lists oauthSession among documented config keys.

^{Reviewed by Cursor Bugbot for commit 67ee6c3. Configure here.}