[LunaUrsa]

Summary

Use the installed TripSit drug database as the combo checker’s source and remove the stale local matrix. Map the DXM label to the database’s dextromethorphan key.

Closes #292

Type of change

• Bug fix

Checklist

• Branch is based on uat and targets uat
• Lint passes (npx eslint .)
• npx next build succeeds locally
• No secrets, .env values, or user data included

Test plan

• Added regression tests for DXM + MXE in both orders. They assert the Unsafe rating and the serotonin syndrome note.
• Direct assertions against the updated module passed for both orders and confirmed every selectable pair resolves.
• Jest could not start locally because Node could not read a dependency through the Windows UNC checkout.