feat(ios): add Swift Package Manager support

[TeddyYeung]

Why

Flutter 3.44+ makes Swift Package Manager (SPM) the default for iOS builds. CocoaPods trunk will be read-only from December 2, 2026. Plugins without SPM support will require users to pass --disable-swift-package-manager on every build.

This PR adds iOS SPM support to flutter_foreground_task so it works seamlessly with modern Flutter toolchains.

What changed

• Added ios/flutter_foreground_task/Package.swift — SPM manifest (swift-tools-version 5.9, iOS 12.0 minimum)
• Added ios/flutter_foreground_task/Sources/flutter_foreground_task/ — Swift-only SPM target (mirrors Classes/ Swift files, with explicit import Flutter / import UserNotifications added to files that relied on CocoaPods umbrella header auto-imports)
• Updated ios/flutter_foreground_task.podspec — iOS platform 8.0 → 12.0
• Updated pubspec.yaml — iOS pluginClass: SwiftFlutterForegroundTaskPlugin (direct Swift registration for SPM)
• Updated CHANGELOG.md — 9.2.3 entry
• Updated .gitignore — added .build/ and .swiftpm/

Architecture note

SPM does not support mixed-language targets (ObjC + Swift in the same target). The solution:

• SPM target: Swift files only (Sources/flutter_foreground_task/)
• CocoaPods: uses existing ios/Classes/ with ObjC wrapper + Swift implementation (unchanged)

Import fixes in SPM copies

Files in ios/Classes/ rely on the ObjC umbrella header to transitively import Flutter and UserNotifications. In the SPM target these frameworks are not auto-imported, so two files were updated with explicit imports:

• service/ForegroundTask.swift — added import Flutter
• service/ForegroundTaskLifecycleListeners.swift — added import Flutter
• service/NotificationPermissionManager.swift — added import UserNotifications

Testing

• ✅ flutter build ios --no-codesign (SPM enabled via flutter config --enable-swift-package-manager) — Build succeeded
• ✅ flutter build ios --no-codesign (SPM disabled) — Build succeeded

Tested with Flutter 3.35.7 on macOS.

Breaking Changes

None. CocoaPods behavior is unchanged.

References

• Flutter SPM guide: https://docs.flutter.dev/packages-and-plugins/swift-package-manager/for-plugin-authors