Add a non-AW command package fixture to prove generator portability

[rickardvh]

Origin: rickardvh/agentic-workspace#1253

Current status

This issue is partially served by later callable/conformance work, especially command-generation #15, which added non-AW fixture coverage for callable generation. Keep this issue open only for portability proof that is still broader than that slice.

Remaining intent

Prove the generator is portable outside AW-shaped assumptions across package metadata, target rendering, primitive registry extension, and non-Python execution surfaces.

Acceptance

• A minimal non-AW command package fixture exercises parser/help generation.
• The fixture exercises primitive registry extension rather than relying only on built-in AW-shaped primitives.
• The fixture exercises at least one target renderer beyond the Python callable path already covered by Generate Python operation callables #15.
• The fixture does not depend on AW operation ids, resource roots, package names, or runtime support files.
• A conformance/check path fails if AW-specific assumptions are required.

Out of scope

• Repeating the already-landed non-AW callable fixture proof from Generate Python operation callables #15 without adding coverage for the remaining portability dimensions.