Add Tooltip to Explain Adjusted Amount in Next Invoice Section

🔍 Problem Statement
As an admin, I experience the Next Invoice amount differing from expected without any explanation, causing confusion and unnecessary support escalations when coupons or balance adjustments are applied.

💡 User Story
As an admin, I want a tooltip on the Next Invoice amount that explains any adjustments, so that I understand the final amount without contacting support.

🎯 Definition of Done
- Given a Next Invoice with adjustments applied, when hovering over the amount, then a tooltip lists each contributing adjustment (coupon, credit balance, etc.).
- This change impacts the UI (Next Invoice tooltip) and API (next invoice response — return itemized adjustments).
- Limitations: covers applied coupons and credit balance only; tax breakdowns are out of scope for v1.

Problem Statement Admins may see a Next Invoice amount that does not match their expectations because it has been adjusted by factors such as applied coupons or existing customer balance . Currently, there is no contextual explanation for these adjustments, which can lead to confusion, support tickets, and reduced trust in billing transparency. User Story As an admin, I want to understand why my upcoming invoice amount is different from the standard price, So that I can clearly see if discounts (coupons) or my account balance have been applied and trust the billing information displayed.