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/next.config.ts

@@ -2,7 +2,7 @@ import type { NextConfig } from 'next';
 import createNextIntlPlugin from 'next-intl/plugin';
 
 // Initialize next-intl plugin with i18n request config path
-const withNextIntl = createNextIntlPlugin('./src/i18n/request.ts');
+const withNextIntl = createNextIntlPlugin('./src/lib/i18n/request.ts');
 
 const nextConfig: NextConfig = {
   output: 'standalone',