Feat/stats dashboard

[kbtale]

Summary

Refactors the Stats and Analytics system to strictly adhere to existing codebase standards and UI modal architecture:

• Replaced the full-screen view with an accessible modal dialog (StatsModal) identical in structure, animations, and focus management to SettingsModal.
• Added a <FUIButton id="stats-open-btn"> in the top header placed immediately next to Settings
• Cleaned the left sidebar so it remains strictly dedicated to interactive tools and category navigation.
• Eliminated all emojis and badge code constructs: achievements are pure text entries with localized title, description, progress meter, and unlock status.
• Styled all components using theme CSS variables (--bg-canvas, --line-color, --text-main, --text-dim, etc.)

Type of Change

• Bug fix
• New feature
• Refactoring
• Performance improvement
• Accessibility improvement
• Documentation update

Checklist

• npm run check passes (Biome lint & format: 222 files checked, 0 errors, 0 warnings)
• npm run test passes (34 test files, 174 tests passing)
• npm run build passes (TypeScript strict mode & Vite production build)
• New i18n keys added to all 3 locales (en, es, it)
• No inline styles added (use SCSS modules)