fix(ios): migrate to UIScene lifecycle

[ilteen]

Summary

• raise the iOS deployment target to 15.0 for Xcode 27 compatibility
• migrate the app to the required UIScene lifecycle
• register Flutter plugins and custom method channels through FlutterImplicitEngineDelegate
• exclude generated platform and build directories from Dart analysis

Testing

• flutter analyze
• flutter build ios --debug --no-codesign
• installed and launched a signed release build on an iOS 27 device

Lockfiles are intentionally excluded.

[github-actions]

Visit the preview URL for this PR (updated for commit eeaf0b0):

https://open-earable-web--pr299-codex-ios-27-uiscene-w21fow7b.web.app

_{(expires Tue, 20 Oct 2026 08:07:40 GMT)}

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[github-actions]

PR Build Artifacts

• Android APK: Download Android APK
• Linux Bundle: Download Linux Bundle
• Windows Runner: Download Windows Runner
• Web Bundle: Download Web Bundle

Full workflow run: https://github.com/OpenEarable/app/actions/runs/35702843040