Inventory optional ModelExpress artifacts in the software manifest

[ankanand-nv]

Description

Add ModelExpress to the generated software inventory as an optional compute-plane
add-on.

Definition of Done

• Catalog entries exist for the chart and the server image, both on the compute
  plane and both marked optional.
• Rows render in the correct generated sections, with distribution and upstream
  source populated.
• Distributions point at the upstream chart repository and container registry.
• Both entries carry version: supported, following the existing catalog
  entries for components that are not pinned by the stack. Exact tested versions
  stay in the guide and the sample.
• docs/user/image-mirroring.md is unchanged.
• No generator source or test changes.
• Manifest generation passes in CI.

Resources

Schema and static-entry precedent: docs/version-catalog/main.yaml
Generated output: docs/user/manifest.md

The generator cannot run against the public mirror locally, because
imports.yaml is absent by design. CI output is the source of truth for the
generated file, so the generated manifest.md in this change should be treated
as provisional until CI regenerates it.

The schema has no Python package kind, so the Python client is not listed unless
a schema owner rules otherwise.

Part of #1113.