feat(ios): enable ai button (#13422)

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

## Summary by CodeRabbit

* **New Features**
* The AI button feature on mobile is now enabled by default only on iOS
devices, instead of being limited to canary builds.
  
* **Chores**
  * Updated internal configuration for mobile feature availability.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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

@@ -209,8 +209,8 @@ export const AFFINE_FLAGS = {
     category: 'affine',
     displayName: 'Enable AI Button',
     description: 'Enable AI Button on mobile',
-    configurable: BUILD_CONFIG.isMobileEdition && isCanaryBuild,
-    defaultState: false,
+    configurable: BUILD_CONFIG.isMobileEdition && BUILD_CONFIG.isIOS,
+    defaultState: BUILD_CONFIG.isMobileEdition && BUILD_CONFIG.isIOS,
   },
   enable_turbo_renderer: {
     category: 'blocksuite',