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.

web/js/api.js

@@ -99,6 +99,7 @@ export const api = {
   cmfStatus: () => j("GET", "/cmf"),
   cmfInstall: () => j("POST", "/cmf/install"),
   cmfPortCheck: (port) => j("GET", "/cmf/port?port=" + encodeURIComponent(port)),
+  cmfFiles: () => j("GET", "/cmf/files"),
 
   // CMF model factory (HuggingFace → local .cmf)
   hfSearch: (q, limit = 24) =>