Refactor i18n setup and improve structure for maintainability

- Relocated `i18n` configuration files to `src/lib/i18n` for better organization.
- Removed obsolete `request.ts` and `routing.ts` files, simplifying `i18n` setup within the project.
- Added extensive tests for `i18n/utils` to validate locale-related utilities, including locale name, native name, and flag retrieval.
- Introduced a detailed `I18N_IMPLEMENTATION_PLAN.md` to document implementation phases, decisions, and recommendations for future extensions.
- Enhanced TypeScript definitions and modularity across i18n utilities for improved developer experience.

frontend/jest.config.js

@@ -14,7 +14,7 @@ const customJestConfig = {
   },
   testMatch: ['<rootDir>/tests/**/*.test.ts', '<rootDir>/tests/**/*.test.tsx'],
   transformIgnorePatterns: [
-    'node_modules/(?!(react-syntax-highlighter|refractor|hastscript|hast-.*|unist-.*|property-information|space-separated-tokens|comma-separated-tokens|web-namespaces)/)',
+    'node_modules/(?!(react-syntax-highlighter|refractor|hastscript|hast-.*|unist-.*|property-information|space-separated-tokens|comma-separated-tokens|web-namespaces|next-intl|use-intl)/)',
   ],
   collectCoverageFrom: [
     'src/**/*.{js,jsx,ts,tsx}',