chore: remove unused MidMarketRate import from main.py

[devin-ai-integration]

chore: remove unused MidMarketRate import from main.py

Summary

Removes the unused MidMarketRate symbol from the database.models import in main.py. The symbol is never referenced in any function, query, or expression in the file. The MidMarketRate model class itself remains in database/models.py and is unaffected.

Review & Testing Checklist for Human

• Confirm MidMarketRate is not referenced anywhere in main.py (e.g., via grep or IDE find-usages)

Notes

• Candidate ID: 1c8517986dfe
• Link to Devin Session
• Requested by: bot_apk

[devin-ai-integration]

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