feat(core): enable battery save mode for mobile (#13441)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
  * Battery save mode is now enabled by default on mobile devices.
* Users will see an updated, more detailed description for battery save
mode.
* Battery save mode can now be configured by all users, not just in
certain builds.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/modules/feature-flag/constant.ts

@@ -286,9 +286,10 @@ export const AFFINE_FLAGS = {
   enable_battery_save_mode: {
     category: 'affine',
     displayName: 'Enable Battery Save Mode (Require Restart)',
-    description: 'Enable battery save mode',
-    configurable: isCanaryBuild,
-    defaultState: false,
+    description:
+      'Limit indexing and other compute-intensive tasks on this device, may experience longer loading time and latency in search and other features, in exchange for quietness.',
+    configurable: true,
+    defaultState: isMobile,
   },
   enable_mobile_database_editing: {
     category: 'blocksuite',