feat(models): port GLM-4V MoE (ViT + GLM-4 MoE text)

[inureyes]

Summary

Add GLM-4V MoE support to mlxcel. Its upstream model_type is glm4v_moe. mlxcel currently has no arm for it in src/models/detection.rs, so a glm4v_moe checkpoint errors "Unsupported model type".

What it is

MoE variant of GLM-4V (GLM-4.5V-class); ViT vision + GLM-4 MoE text backbone.

In-tree reuse

GLM-4 MoE text src/models/glm4_moe.rs, plus the GLM-4V vision encoder from the sibling port.

Scope

• Add the ModelType variant + detection.rs arm for glm4v_moe.
• MoE wiring on the GLM-4V vision path.
• Register across the arch/metadata tables; update docs/supported-models.md; add tests + validate on a real checkpoint.

Effort: medium