Added EUR support, fallback provider, caching, and currency tracking.

[dimitriyTsemma]

Summary

This PR implements EUR currency support, adds a fallback exchange rate provider, implements smart caching with daily invalidation, and tracks catalog currency usage via asynchronous jobs.

Changes

🆕 New Features

1. EUR Currency Support

   • Added GET /api/catalog/EUR endpoint for product catalog with EUR prices
   • Added GET /api/exchangeRate/EUR endpoint for EUR/UAH exchange rate
   • Updated validation to accept usd, uah, and eur currencies

2. Fallback Exchange Rate Provider

   • Integrated Open Exchange Rates API (https://open.er-api.com/v6/latest/UAH) as secondary provider
   • Implemented automatic fallback using Chain of Responsibility pattern
   • Primary: NBU API, Fallback: Open Exchange Rates API

3. Smart Caching

   • 10-minute TTL for exchange rates
   • Automatic cache invalidation on a new calendar day
   • Configurable cache driver (Redis/Memcached/Database)
   • Implemented via Decorator pattern

4. Currency Usage Tracking

   • Asynchronous job dispatched on every catalog request
   • Tracks: currency, timestamp, IP address, user agent
   • Database table: catalog_currency_usage with indexed columns

5. Configuration-Driven Architecture

   • Created config/currency.php for provider selection
   • Swap providers without code changes via environment variables
   • Configurable caching behavior

🏗️ Architecture & Design Patterns

• Strategy Pattern — CurrencyRateProviderInterface for interchangeable providers
• Chain of Responsibility — ChainOfResponsibilityProvider for automatic fallback
• Decorator Pattern — CachedCurrencyRateProvider for transparent caching
• Dependency Inversion — Application depends on abstractions, not implementations
• SOLID Principles — Applied throughout the codebase

Test Plan

✅ All Tests Passing

php artisan test