Fix migration runner to use custom script

[nicholaspsmith]

Summary

This is a hotfix to resolve production study sessions which are broken because the migration didn't run properly. The custom db-migrate.ts script uses the _migrations table which matches the production setup and ensures migrations are applied correctly.

Details

• Updated migration runner to use the custom db-migrate.ts script instead of relying on the default drizzle migration mechanism
• The custom script properly handles the _migrations table tracking that production uses
• This restores functionality to study sessions that were blocked by missing migrations

Testing

• Pre-push checks and unit tests passed
• Ready for review and merge

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