Fix scan findings: price_aggregates table, env vars, zero-div checks - #10

No actionable issues found.

This pull request adds the missing price_aggregates table to the database schema initialization in database.rs. It modifies the Shanghai price service to configure its update interval via the UPDATE_INTERVAL_SECONDS environment variable instead of using a hardcoded value. Additionally, it inserts a zero-check before division in the bot's price calculation logic to prevent potential runtime errors when the western price is zero. Lastly, it removes a duplicate comment in bot.rs for improved code clarity.