<!-- This is an auto-generated comment: release notes by coderabbit.ai
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## Summary by CodeRabbit
* **New Features**
* Added a global API to check the AI button feature flag status.
* **Bug Fixes**
* Improved handling for the AI button feature: the app now checks the
feature flag before proceeding and provides a clear error if the feature
is disabled.
* **Refactor**
* Removed all AI button presentation and dismissal logic from the app.
* Deleted unused plugin interfaces and registration related to the AI
button feature.
* **Chores**
* Updated project metadata and build configuration for iOS.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
close AF-1663, AF-1756
- new global `ModalConfigContext`
- new logic to judge whether inside modal
- render `✕` for PageHeader back if inside modal
- only enable `NavigationGesture` when there is `<` in PageHeader
