refactor: home card accessibility & design

[vachmara]

🔗 Linked issue

❓ Type of change

• [ ] 📖 Documentation (updates to the documentation or readme)
• [ ] 🐞 Bug fix (a non-breaking change that fixes an issue)
• [x] 👌 Enhancement (improving an existing functionality)
• [ ] ✨ New feature (a non-breaking change that adds functionality)
• [ ] 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• [ ] ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This pull request refactors several UI components for improved code clarity, accessibility, and consistency, especially around HomeCard component.

UI Refactoring and Button Improvements:

• Replaced custom anchor tags with standardized UButton props such as to, label, and external for navigation actions (GitHub/Discord connect, profile sharing), improving accessibility and maintainability.
• Updated event handling for logout and profile sharing buttons to use Vue’s .stop modifier for click events, ensuring proper event propagation control.
• Standardized button color and variant usage for Discord badge unlocking and profile sharing actions, removing conditional class logic and using consistent props.

Code and Style Cleanup:

• Removed the entire <style> block from HomeCard.vue, eliminating unused and redundant CSS classes related to card, button, and checkbox styling.
• Minor adjustment in app.config.ts to simplify the button border class definition by removing a redundant border width specification.

Minor UI Consistency Fixes:

• Updated avatar image sources to use contributor.username directly, ensuring consistent avatar rendering.
• Fixed utility class usage in profile card backgrounds for consistent styling across breakpoints and hover states in [username].vue.