### Check for existing issues

- [x] I have searched the existing issues and checked that my issue is not a duplicate.

### What happened?

When deleting a customer via `/customer/delete`, the Redis counter `spend:end_user:{id}` is not deleted or reset. When re-creating a customer with the same `user_id`, the new customer starts with the old spend value from Redis.

**Example:** 1. Create customer, make request -> `spend` becomes 0.000128 2. `/customer/delete` 3. `/customer/new` (same user_id, new budget) 4. `/customer/info` shows `spend: 0.0` (DB query, correct) 5. Budget check fails: "ExceededBudget: Spend=0.000128, Budget=0.00001" (Redis counter, wrong!)

Expected: `/customer/delete` should remove `spend:end_user:{id}` from Redis.

### Steps to Reproduce

When deleting a customer via `/customer/delete`, the Redis counter `spend:end_user:{id}` is not deleted or reset. When re-creating a customer with the same `user_id`, the new customer starts with the old spend value from Redis.

**Example:** 1. Create customer, make request -> `spend` becomes 0.000128 2. `/customer/delete` 3. `/customer/new` (same user_id, new budget) 4. `/customer/info` shows `spend: 0.0` (DB query, correct) 5…