Fix: db_cleanup pool, error logging, cleanup unused vars

[buzzkillb]

Summary

• db_cleanup now uses shared connection pool instead of opening its own connection
• Log errors in aggregation instead of silently using fallback values
• Remove unused variables (_effective_start in health.rs, DATABASE_PATH import)

Changes

• DatabaseCleanup accepts Arc and uses its connection pool
• Aggregation errors are now logged with warn! instead of silently falling back
• Removed unused _effective_start variable in health.rs
• Removed unused DATABASE_PATH import in db_cleanup.rs
• Fixed unused start_time variable warning

Note

Low Risk

Overview
This pull request makes three main improvements: refactors db_cleanup to use a shared connection pool from PriceDatabase instead of creating its own connection, adds proper error logging in the aggregation logic using warn! instead of silently falling back to default values, and removes unused variables including _effective_start from health.rs and the unused DATABASE_PATH import.

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