feat: implement async database session management and CBSL currency exchange rate service with persistent caching

feat: implement key-less FX service with native CBSL web scraping and fallback cache logic

feat: implement FX service with persistent caching and optimize concurrent rate fetching in main

fix: restore standard connection session for Telegram bot and FX rate fetching to enable NAT64 routing on Hugging Face Spaces

feat: implement FXService and force IPv4 connectivity for bot and API requests

Fix markdown parsing, asyncpg prepared statements, and flexible command arguments

first commit