✨ feat(visual): transport icons overhaul and dark mode migration to M3 2025

[MasuRii]

📝 Summary

This PR implements comprehensive visual improvements for PH Fare Calculator v2.4.0, including a complete transport icon overhaul with unique icons for all 12 Philippine transport modes, dark mode migration to Material Design 3 2025 standards, and app logo configuration fixes.

✨ Changes

1. Transport Mode Icons - Unique Icons for All 12 Modes

• Created TransportIconService with centralized icon management
• All 12 transport modes now have unique icons (Jeepney, FX/Taxi, Bus, UV Express, Tricycle, Motorcycle, LRT Line 1, LRT Line 2, MRT Line 3, PNR, Ferry, and Airport Rail)
• Added TransportIconStyle enum supporting 4 variants: filled, rounded, outlined, sharp
• Updated 3 widgets to use the centralized service: fare_result_card.dart, fare_results_list.dart, transport_mode_selection_modal.dart
• Added 51 comprehensive unit tests achieving 81.8% coverage

2. Dark Mode - 2025 Material Design 3 Standards

• Migrated from #001216 (Abyss) to #121212 baseline
• Implemented 7-layer surface container system (#161616 - #2C2C2C)
• Eliminates halation and eye strain while maintaining OLED efficiency
• WCAG AA compliant with 16:1 contrast ratios

3. App Logo - Fixed Configuration

• Updated flutter_launcher_icons with correct asset paths
• Regenerated native icons for Android (adaptive icons) and iOS
• Background: Philippine Flag Blue (#0038A8)
• Added colors.xml for Android color resources

Additional Improvements

• Security: Fixed .env exposure by removing from assets, added null safety in fare_formula.dart
• Documentation: Updated CHANGELOG.md and README.md
• Version: Bumped to 2.4.0 in pubspec.yaml

📁 Files Changed

File	Type	Impact
lib/src/core/constants/transport_icon_style.dart	✨ New	TransportIconStyle enum definition
lib/src/core/constants/transport_icons.dart	✨ New	TransportIconService implementation (284 lines)
lib/src/core/theme/app_theme.dart	🐛 Fix	Dark mode M3 migration, surface container system
lib/src/core/theme/transit_colors.dart	♻️ Refactor	Color system updates
lib/src/models/fare_formula.dart	🐛 Fix	Null safety improvements
lib/src/presentation/widgets/fare_result_card.dart	♻️ Refactor	Updated to use TransportIconService
lib/src/presentation/widgets/main_screen/fare_results_list.dart	♻️ Refactor	Updated to use TransportIconService
lib/src/presentation/widgets/main_screen/transport_mode_selection_modal.dart	♻️ Refactor	Updated to use TransportIconService
pubspec.yaml	📦 Build	Version bump to 2.4.0
android/app/src/main/res/drawable-*/ic_launcher_foreground.png	✨ New	Android adaptive icon foregrounds
android/app/src/main/res/mipmap-anydpi-v26/	✨ New	Android adaptive icon configuration
ios/Runner/Assets.xcassets/AppIcon.appiconset/	📦 Build	Regenerated iOS app icons
test/services/transport_icon_service_test.dart	🚦 Test	51 unit tests (81.8% coverage)
CHANGELOG.md	📚 Docs	v2.4.0 release notes
README.md	📚 Docs	Updated documentation

🧪 Testing Performed

• ✅ 422 tests passing across the test suite
• ✅ 51 TransportIconService unit tests with 81.8% coverage
• ✅ All existing functionality preserved
• ✅ Dark mode WCAG AA compliant (16:1 contrast ratios)
• ✅ Android adaptive icons verified
• ✅ iOS app icon configuration verified

📋 Checklist for Reviewers

• Transport icons render correctly for all 12 modes
• Dark mode surfaces are consistent and comfortable
• App logo displays correctly on both platforms
• All tests pass
• No regressions in existing functionality

🔗 Related Issues

This PR addresses the visual improvements milestone for v2.4.0 release.

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Type: enhancement/feature
Breaking Changes: TransportIconService replaces hardcoded icon mappings (existing code using hardcoded icons will need migration)