feat: centralize color management with const-compatible ColorConstants class and comprehensive documentation

[Charmiseera]

feat: centralize color management - replace scattered hardcoded colors with ColorConstants class across 11 files

What kind of change does this PR introduce?

Feature/Refactoring - This PR introduces a centralized color management system to improve code maintainability and consistency.

Issue Number:

Fixes #85

Snapshots/ video:

screen-capture.mp4

• ✅ Build Status: flutter build web - Successful
• ✅ Runtime Status: flutter run -d chrome - Working
• ✅ No Breaking Changes: All existing functionality preserved
• ✅ Code Quality: All lint issues resolved

Summary

This PR addresses the issue of scattered hardcoded color values throughout the codebase by implementing a comprehensive centralized color management system.

Problems Solved:

• Eliminated 20+ scattered Color(0xFFxxxxxx) hardcoded values
• Fixed Colors.grey[shade] const evaluation errors
• Improved code maintainability and consistency
• Established single source of truth for all application colors

Key Changes:

• New: color_constants.dart - Central color definitions with 33 organized constants
• Updated: 11 existing files to use centralized color references
• Categories: 6 functional color groups (Background, Snackbar, UI, Highlight, Dialog, App-specific)
• Documentation: Added comprehensive CONTRIBUTION_SUMMARY.md
• Fixes: highlightColors now fully const-compatible, checkIconWhite color centralized, gray color references made semantic

Files Modified:

• color_constants.dart (new & improved)
• canvas_state.dart & lib/cubit/canvas_cubit.dart
• lib/ui/widgets/ - 5 widget files updated
• lib/ui/screens/ - 3 screen files updated
• custom_snackbar.dart
• CONTRIBUTION_SUMMARY.md (new)
• pubspec.lock, pubspec.yaml (dependency upgrades for lockfile update)

Does this PR introduce a breaking change?

No - This PR does not introduce any breaking changes. All existing functionality is preserved while improving the underlying code organization. The changes are purely internal refactoring with no API or behavior modifications.

Other information

Benefits:

• Maintainability: Easy color scheme updates in single file
• Performance: Compile-time const optimizations
• Consistency: Standardized color usage across all components
• Developer Experience: Clear color naming and documentation
• Future-Ready: Simplified theme customization and updates

Technical Details:

• All colors are static const for compile-time optimization
• Semantic naming convention (purpose-based, not appearance-based)
• Comprehensive inline documentation
• Helper methods for common color operations
• Backward compatible with existing Material Design colors

Have you read the contributing guide , README.md , code of conduct?

Yes - All contribution guidelines, project documentation, and code of conduct have been reviewed and followed.

[github-actions]

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[github-actions]

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[may-tas]

Is there any particular reason for this removal? if not then please add it back.

[may-tas]

@Charmiseera

[may-tas]

Please remove this line.

[may-tas]

@Charmiseera

[Charmiseera]

Ok

[may-tas]

@Charmiseera Kindly upload a screen recording as proof of work.
To verify if the colors in the user interface are consistent.

[Charmiseera]

@Charmiseera Kindly upload a screen recording as proof of work. To verify if the colors in the user interface are consistent.

Sure

[may-tas]

@Charmiseera updates?

[Charmiseera]

I will update code as you suggested and upload working proof by today night.

[may-tas]

Alright.

[Charmiseera]

Alright.

Hey @may-tas , I have updated the code and also uploaded the screen recording as working proof.

[may-tas]

@Charmiseera
Great work! Centralising the colours will improve code quality and stability.