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/i18n/locales/en.json

@@ -31,6 +31,8 @@
     "action_delete": "Delete",
     "action_add": "Add environment",
     "action_edit": "Edit",
+    "action_export": "Export",
+    "action_import": "Import",
     "action_save": "Create",
     "action_update": "Save",
     "action_cancel": "Cancel",