feat(models): ask whether to delete the model file from disk

- The delete button now opens a dialog; for local models it includes an "also
  delete the model file from disk" checkbox (checked by default), so a pool
  entry can be removed while keeping the .cmf for later.
- DELETE /admin/api/models/:id accepts ?delete_file=true|false (default true).
  The shared-file guard still applies: a file referenced by another model is
  never removed.
- cmf_file_for_model now treats any loopback base_url as local (managed servers
  can sit on any port, not just the legacy local_port).

web/js/api.js

@@ -60,7 +60,8 @@ export const api = {
   listModels: () => j("GET", "/models"),
   createModel: (b) => j("POST", "/models", b),
   updateModel: (id, b) => j("PUT", "/models/" + encodeURIComponent(id), b),
-  deleteModel: (id) => j("DELETE", "/models/" + encodeURIComponent(id)),
+  deleteModel: (id, deleteFile = true) =>
+    j("DELETE", "/models/" + encodeURIComponent(id) + "?delete_file=" + (deleteFile ? "true" : "false")),
   probeModel: (id) => j("POST", "/models/" + encodeURIComponent(id) + "/probe"),
 
   // routing