chore: add clearAll button, iOS run script, and simplify build guide

[fadi-george]

Description

One Line Summary

Add a Clear All notifications button to the demo app, an iOS simulator run script, and simplify the build guide to reference the shared sdk-shared docs.

Details

Motivation

The demo app was missing a way to clear all delivered notifications. A helper script for iOS simulator selection was also needed to match the existing Android one. The build guide was duplicating content that now lives in the shared sdk-shared/demo/build.md.

Scope

Demo app changes

• onesignal_repository.dart adds clearAllNotifications() calling OneSignal.Notifications.clearAll()
• app_viewmodel.dart adds clearAllNotifications() with log and snackbar feedback
• send_push_section.dart adds a CLEAR ALL button (outlined/destructive style)

iOS run script

• examples/run-ios.sh lists booted iOS simulators and lets you pick one, then runs flutter run -d <udid>
• examples/demo/README.md updated to reference the new script

Build guide

• examples/build.md now references the shared sdk-shared/demo/build.md and only contains Flutter-specific overrides

Testing

Manual testing

Ran the demo app on Android emulator. Verified the CLEAR ALL button clears delivered notifications. Tested run-ios.sh with a booted iOS simulator.

Affected code checklist

• Notifications
  • Display
• Public API changes

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

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