Finish or hide the generic list-variable scaffold

[blackopsrepl]

Summary

The CLI advertises a generic list-variable scaffold path that intentionally errors at runtime.

Problem

solverforge new --list is presented to users even though the generic list template is still “coming soon”.

Why This Matters

Advertised scaffolding flows should exist, or they should not appear as available options.

Proposed Work

• Implement the generic list scaffold, or
• Hide/remove the --list path until the template is actually supported.

Acceptance Criteria

• solverforge new --list either succeeds with a supported template or is not presented as an available option.
• CLI docs and examples match runtime behavior.

Source

Derived from PR #3 (PRODUCTION_REVIEW_ISSUES_2026-03-20.md).

[blackopsrepl]

Already WIP, needs to be merged here.

[blackopsrepl]

Resolved by #17.

We gated the generic list scaffold so bare --list is no longer treated as a supported path, kept --list=vehicle-routing available, and preserved the specialized guidance for users who invoke the unsupported generic form.