Python rewrite with charts and slash commands - #16

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This pull request performs a complete rewrite of the RustyMcPriceface Discord bot from Rust to Python. The new implementation replaces the Rust backend with Python services using discord.py for the bot, asyncpg for PostgreSQL database operations, matplotlib for chart generation, and aiohttp for price fetching from Pyth Network. The bot now supports Discord slash commands (/price current and /chart price) with price charts featuring high/low markers, percentage changes, and cryptocurrency conversions. Configuration has been updated to use PostgreSQL instead of SQLite, and Docker Compose has been modified to include a PostgreSQL service alongside the bot container. The CI/CD workflow has been rewritten from Rust cargo tests to Python linting with ruff and Docker smoke tests.
Based on my analysis of this complete rewrite PR, the significant runtime defects have already been identified in earlier review comments. This PR replaces the Rust implementation with Python using discord.py for slash commands, PostgreSQL for persistence, and matplotlib for chart generation. The main infrastructure changes include switching from SQLite to PostgreSQL with docker-compose, adding Discord slash commands for price and chart queries, and introducing a new chart service for visual price history display. The Python implementation maintains similar data flow patterns to the Rust version with periodic price updates, presence updates, and database-backed price history.