Evaluate Mars AppImage or portable Linux packaging

[luccahuguet]

A portable Linux artifact could help non-Nix testing, but GPU loader behavior, dependency bundling, fonts, desktop integration, and terminfo expectations need an explicit support decision.

Internal tracking: Bead yzt-clean-rio-rebuild-0kz.15.4.

Scope:

• Decide whether Mars should ship an AppImage or equivalent portable Linux package.
• Define what is bundled versus required from the host, especially Vulkan loader, GPU ICDs, fonts, desktop metadata, and terminfo.
• Plan or add a smoke test that separates host graphics runtime failure from Mars crash.
• Avoid describing portable packaging as supported until an artifact is validated.

Acceptance:

• AppImage/portable support is accepted, deferred, or rejected with concrete reasoning.
• If accepted, follow-up work names tooling, artifact naming, runtime assumptions, and smoke verification.
• Documentation states current support boundaries clearly.