[ENGT-5159] Verify packaged documentation works offline

[navkul]

Summary

• pack the already-built @grepr/cli npm artifact in the publish workflow
• install that tarball into an isolated prefix
• run docs:get inside a network namespace with no external interfaces
• assert a known bundled documentation page contains its expected heading

Depends on grepr/grepr-server#4423.

Fixes ENGT-5159

Why

The upstream unit test uses a synthetic local index, while the existing artifact tests only exercise help and version commands. A missing or corrupt docs-index could therefore reach the npm package without failing CI.

This regression test exercises the packed npm artifact itself and proves docs:get can retrieve bundled content without downloading the embedding model or reaching another service. The existing npm publish behavior remains unchanged.

Validation

• Workflow YAML parses successfully
• git diff --check passes
• Branch contains only the offline packed-artifact regression
• GitHub Actions workflow passes with grepr/grepr-server#4423

[notion-workspace]

Fix offline CLI documentation commands