Add cache layer to CLI help remark plugin for CI builds

The remark plugin generates --help output at build time, but fails in CI
where the QIT CLI isn't available (managed commands require auth). Now the
plugin writes a .cli-help-cache.json when building locally and reads from
it when the CLI is unavailable, so CI deploys use cached help output.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Luc45