models scan: one models--* husk dir makes the whole store read as an empty HF cache #138

A model root that contains a single HuggingFace-cache-style directory is classified as an HF cache, even when that directory is an abandoned husk with no content. The HF-cache scan then finds no refs/blobs and the store reports zero models.

Repro (Windows, LM Studio store): F:\AI\.lmstudio\models contained 14 regular model directories (43 models, 391.6 GiB) plus one empty husk from an abandoned HF download:

models--mradermacher--Qwen3.5-9B-Nikusui-v1-i1-GGUF/
(no files at all — no refs/, no blobs/)

/v1/models and berth models reported 0 models. Removing only the husk (all 43 real models untouched) made the same scan report all 43.

So sourceOf() in internal/models/scan.go classifies the root by the presence of one models--* directory, and scanHFCache() ignores everything that is not in refs/blobs layout. One abandoned download shadows the whole store.

Suggestion: only classify a root as an HF cache when it actually has HF cache structure (refs/ or blobs/); scan the rest as a plain directory, or scan both layouts and merge.