idea: Allow attaching an MTP draft GGUF when importing a local model

[DorukTaneli]

Problem Statement

#8304 added external MTP support, but only for Hub downloads. The Import Model dialog for local files only accepts a main GGUF and an optional mmproj, so locally imported models can't use a separate MTP draft GGUF.

Feature Idea

Add an optional MTP file picker to the Import Model dialog, mirroring the existing mmproj picker. The backend already handles this (pullModel accepts mtpPath and the llamacpp extension processes local MTP files), so only the dialog UI is missing.

I'd be happy to submit a PR for this!