feat(app): add environment import/export and sidebar footer info

- add environment import/export API endpoints and client integration

- add environment export actions and toolbar import/export buttons in UI

- move theme switcher to sidebar bottom and show root package version

- switch snippet card menu icon to cog for consistent options affordance

client/src/api/client.ts

@@ -133,6 +133,15 @@ export const environments = {
   remove(id: string): Promise<void> {
     return request(`/environments/${id}`, { method: 'DELETE' });
   },
+  exportEnvironment(id: string): Promise<unknown> {
+    return request(`/environments/${id}/export`);
+  },
+  importEnvironment(payload: unknown): Promise<Environment> {
+    return request('/environments/import', {
+      method: 'POST',
+      body: JSON.stringify(payload),
+    });
+  },
 };
 
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