Add flip board button to puzzle screen (#3372)

[assassinaj602]

Description

Added a "Flip board" button to the puzzle screen that allows users to toggle the chess board orientation during puzzle analysis and viewing. This feature is consistent with the existing flip board functionality in the game screen.

Changes Made

• Added _isBoardTurned state variable in _BodyState to track board orientation
• Board orientation toggles between puzzleState.pov and its opposite when flipped
• Added flip board button in the bottom bar when in puzzle view mode (PuzzleMode.view)
• Both portrait and landscape board orientations are supported
• Uses existing l10n.flipBoard translation key (already available across all locales)
• Uses CupertinoIcons.arrow_2_squarepath icon, consistent with other flip buttons

Screenshots/Videos

Screenshots (Click to expand)

Testing

• Tested on Android emulator
• Tested on iOS simulator (if applicable)
• Verified board flips correctly when button is tapped
• Verified puzzle solving still works after flipping
• Verified other puzzle functionality remains unaffected
• Tested in both portrait and landscape orientations
• Tested in puzzle view mode (button visible)
• Tested in puzzle solving mode (button hidden as expected)

Implementation Details

• State location: _isBoardTurned lives in _BodyState so it resets when leaving the screen
• Callback pattern: Uses VoidCallback passed from _BodyState to _BottomBar (consistent with other screens)
• Conditional rendering: Button only appears in PuzzleMode.view mode
• Orientation logic: orientation: _isBoardTurned ? puzzleState.pov.opposite : puzzleState.pov

Related Issue

Fixes #3372

Checklist

• Code follows the project's coding style (functional programming, immutability)
• Changes are tested locally
• No new translations added (using existing l10n key)
• flutter analyze passes (pre-existing errors in file are documented)
• flutter test passes
• Code is formatted with dart format
• Screenshots/video attached (if UI changes)
• PR is in draft mode (ready for review)

Note for Reviewers

The analyzer errors shown are pre-existing in the file (PuzzleSettingsBottomSheet related) and were not introduced by this change. This PR only adds the flip board functionality.

[veloce]

Thanks for contributing @assassinaj602 ! I don't see the screenshot (when I click on expand, nothing happens).