feat: resolve HF Hub cache layout in model directory scanning

[AlexWorland]

Summary

Models downloaded via huggingface-cli or huggingface_hub use an indirect cache layout (models--Org--Name/refs/main → commit hash → snapshots/<hash>/) instead of a flat directory. When a user adds their HF cache directory (e.g., ~/.cache/huggingface/hub) to model directories in settings, the scanner didn't understand this indirection and found nothing.

This change teaches the existing two-level scanner to resolve HF Hub cache entries to their active snapshot. No directories are scanned automatically — users opt in by adding their HF cache path to model directories. The resolved snapshot flows through the same _is_model_dir() → _register_model() pipeline as all other models.

Changes

File	Change
omlx/model_discovery.py	Add _resolve_hf_cache_entry() — resolves models--Org--Name/ to snapshots/<hash>/ via refs/main; integrate into discover_models() between Level 1 and Level 2 checks
omlx/admin/routes.py	Add HF cache resolution to list_hf_models() dashboard endpoint; extract duplicated dedupe/size/append logic into _add_model() helper
tests/test_model_discovery.py	13 new tests — 6 unit tests for _resolve_hf_cache_entry() edge cases, 7 integration tests for discover_models() with HF cache layouts

How it works

discover_models(model_dir):
  for each subdir:
    1. Is it an adapter?           → skip
    2. Has config.json?            → Level 1: register directly
    3. Is it models--Org--Name/?   → NEW: resolve snapshot, register if valid model
    4. Otherwise                   → Level 2: scan as org folder

Existing flat and org-nested layouts are completely unaffected — the HF cache check only fires for directories matching the models--*--* naming pattern, and the continue ensures it doesn't fall through to the org scan.

Testing

tests/test_model_discovery.py    88 passed (75 existing + 13 new)

New test coverage:

• _resolve_hf_cache_entry(): valid entry, regular dir, missing org separator, missing refs/main, missing snapshot, whitespace stripping
• discover_models(): single/multiple HF cache models, model_path points to snapshot, missing config.json skipped, mixed flat+HF cache, mixed org+HF cache, no fallthrough to org scan