Feat: Case Insensitive Coupons (#322)

## Summary 
- Use lowercase in all related to coupons for easy user experience

## Screenshots
### Ref

![ref](https://github.com/user-attachments/assets/fd6520ec-d948-46dc-ac8a-c066b3bd8158)

### Before

![before](https://github.com/user-attachments/assets/63cdf407-98c6-45d9-8331-0a3df06d25ea)

### After

![after](https://github.com/user-attachments/assets/051d4a59-7816-460e-9e75-7002838d3b5f)

Author: joseglego

drizzle/migrations/0038_far_slyde.sql

@@ -0,0 +1,2 @@
+DROP INDEX IF EXISTS "coupons_code_index";--> statement-breakpoint
+CREATE INDEX IF NOT EXISTS "coupons_code_index" ON "coupons" USING btree (lower("coupon"));