Add Daily Puzzle home screen widget for iOS and Android

[Haedong-Jeon]

Summary

• Add a native home screen widget that displays the daily puzzle with a rendered board image, side to move, and play count
• Implement HomeWidgetService in Flutter that listens for daily puzzle updates and board preference changes, then pushes
  data to the native widget via the home_widget package
• iOS widget uses WidgetKit with SwiftUI, supporting both .systemSmall and .systemMedium families; Android widget uses
  Jetpack Glance with Compose
• Tapping the widget opens the app (and navigates to the puzzle via deep link on iOS)

Implementation Details

Flutter (Dart)

• New HomeWidgetService (lib/src/model/home_widget/home_widget_service.dart) started in app.dart alongside other services
• Listens to dailyPuzzleProvider and boardPreferencesProvider to keep the widget in sync
• Renders the chessboard as a static image using StaticChessboard from the chessground package
• Uses App Group (group.org.lichess.mobileV2) for shared data storage between the app and widget extensions

Android

• DailyPuzzleWidget built with Jetpack Glance (androidx.glance:glance-appwidget:1.1.1)
• DailyPuzzleWidgetReceiver extends HomeWidgetGlanceWidgetReceiver
• Widget auto-updates every 24 hours (updatePeriodMillis: 86400000)
• Added Kotlin Compose compiler plugin for Glance support

iOS

• DailyPuzzleWidget WidgetKit extension with TimelineProvider
• Supports systemSmall (board + side to move) and systemMedium (board + side to move + play count + CTA) sizes
• Timeline refreshes hourly
• Configured with shared App Group entitlements for both Runner and widget extension

Dependencies

• Added home_widget: ^0.9.0 to pubspec.yaml

Test plan

• Verify the widget appears in the home screen widget picker on both iOS and Android
• Confirm the board image renders correctly with the user's board theme and piece set
• Change board preferences (theme, piece set) in the app and verify the widget updates
• Test the widget displays "Open Lichess to load" when no puzzle data is available yet
• Verify tapping the widget opens the app
• Test on iOS with both .systemSmall and .systemMedium widget sizes
• Verify the widget updates when a new daily puzzle is available

[veloce]

That is really nice! Thanks for this @Haedong-Jeon

Before I review this (focusing on releasing vs. computer right now), I have a few questions. The "Test plan" section, does it mean that you have already tested it?

It would be nice to share a screen recording to see it in action, if possible on both platform.

Suggestion: it would look nicer with slightly round corners imo :)

[Haedong-Jeon]

"Test Plan" refers to the checklist that you, as the maintainer of this project, need to verify before merging this pull request into the main branch. I've already checked it myself, but you need to check it as well.

Additionally, I felt that some minor feature improvements are needed, including rounding the widget's borders. Therefore, I'll close this pull request and open a new one once the work is complete.

[veloce]

Well noted about the test plan, of course I will test it.
I don't think you need to close the PR for that, you could just add more commits to it, or pass it again into a draft status. But do as you want.

I'd like to see a screen recording of the feature in action if possible, thanks.