BizCore v2.8.1 Live Invoice Calculation Hotfix

INSTALL
1. Upload this ZIP to /public_html/ceylongemx.online/
2. Extract and overwrite.
3. Open https://ceylongemx.online/update-2.8.1.php
4. Click Install v2.8.1 Hotfix.
5. Press Ctrl + F5.

LIVE CALCULATIONS
- Selecting an item fills its selling price automatically.
- Quantity defaults to 1.
- Line total updates when quantity or unit price changes.
- Subtotal updates live.
- Grand Total = Subtotal - Discount + Tax.
- Cash/Card/Bank automatically set Amount Paid equal to Grand Total.
- Credit automatically sets Amount Paid to 0.
- Mixed payment keeps Amount Paid editable.
- Balance and Change are shown live.

SERVER-SIDE VALIDATION
The original v2.8 server-side calculations and stock validation remain active.
The browser calculations are only a faster user interface and do not replace
the secure invoice posting calculations.
