fix: finish 2.9.0 plugin moves and get every check green

plugins/file-manager/src/frontend/host-settings.ts

@@ -0,0 +1,14 @@
+/** One of this plugin's host settings, from the host payload. */
+export function fileManagerHostSetting<T>(
+  host: object | null | undefined,
+  key: "enableFileManager" | "defaultPath" | "scpLegacy",
+  fallback: T,
+): T {
+  const settings = (
+    host as { pluginSettings?: Record<string, Record<string, unknown>> } | null
+  )?.pluginSettings;
+  const value = settings?.["file-manager"]?.[key];
+  return value === undefined || value === null || value === ""
+    ? fallback
+    : (value as T);
+}