### Check for existing issues

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

### What happened?

After creating, updating, or deleting a customer via `/customer/new`, `/customer/update`, or `/customer/delete`, the Redis cache key `end_user_id:{id}` (TTL=300s) is not invalidated. Budget enforcement continues using stale data for up to 5 minutes.

**Example 1 (delete + re-create):** 1. Create customer with `max_budget: 0.00001` 2. Make request -> 429 ExceededBudget (expected) 3. Delete customer, then re-create with same `user_id` but `max_budget: 100.0` 4. Check `/customer/info` -> shows correct `max_budget: 100.0`, `spend: 0.0` 5. Make another request -> **429 ExceededBudget** (WRONG! Still using old budget from cache)

**Example 2 (just update via `/customer/update`):** 1. Create customer with `max_budget: 0.00001` 2. Make request -> spend becomes `0.000128` 3. Make request -> 429 ExceededBudget (expected) 4. Update via `/customer/update` with `max_budget: 100.0` 5. Check `/customer/info` -> shows correct `max_budget: 100.0` 6. Make another request -> **429 ExceededBudget: Spend=0.000128, Budget=1e-05** (WRONG! Cache still has old budget) …