feat(FN-1133): add plugin hot-reload support

- Add PluginLoader hot-load/unload with watch mode, auto-recovery, and staged loading
- Add PluginRunner reactive integration with executor dynamic tools registration
- Add dashboard reload endpoint (POST /api/plugins/reload) and PluginManager UI
- Add comprehensive tests for plugin-hot-reload (core) and plugin-runner (engine)
- Update plugin authoring docs and add memory notes
- Add changeset for @gsxdsm/fusion minor release

packages/dashboard/app/api.ts

@@ -3837,3 +3837,10 @@ export async function updatePluginSettings(
     body: JSON.stringify({ settings }),
   });
 }
+
+/** Reload a running plugin with updated code */
+export async function reloadPlugin(id: string, projectId?: string): Promise<PluginInstallation> {
+  return api<PluginInstallation>(withProjectId(`/plugins/${encodeURIComponent(id)}/reload`, projectId), {
+    method: "POST",
+  });
+}