feat: implement async database session management with auto-migration and historical data seeding

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

Simplify Telegram Bot to unified daily rate list subscription and drop legacy tables

fix: implement NullPool and disable statement caching for PgBouncer compatibility

fix: resolve create_engine type error and use dynamic prepared statement names

fix: disable sqlalchemy prepared statement cache for pgbouncer compatibility

fix: use timezone-naive UTC for created_at to avoid pgsql dataerror

fix: disable prepared statement cache for pgcat/supavisor connection pooler

fix: resolve SQLite/PostgreSQL PgBouncer database parameter mismatch and add self-healing BIGINT migration for Telegram user chat_id

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

feat: implement asynchronous SQLAlchemy database session management and initialization

feat: implement database schema, async session management, and bot command handlers for FlyRates

first commit