feat(settings): pick a local model from a dropdown of existing .cmf files

- New GET /admin/api/cmf/files lists the .cmf files (and tensor-dir .cmf) under
  models_dir, with sizes.
- Settings → Local models: the per-row model field is now a dropdown of those
  files instead of a hand-typed path, and auto-fills the id from the filename.

Cargo.lock

@@ -285,7 +285,7 @@ checksum = "1d07550c9036bf2ae0c684c4297d503f838287c83c53686d05370d0e139ae570"
 
 [[package]]
 name = "cortiq-gateway"
-version = "0.2.8"
+version = "0.2.9"
 dependencies = [
  "anyhow",
  "arc-swap",