BizCore v2.9 Flexible Sales Discount Engine

INSTALL
1. Take full files and database backups.
2. Upload this ZIP to /public_html/ceylongemx.online/
3. Extract and overwrite.
4. Open https://ceylongemx.online/update-2.9.php
5. Click Install v2.9 Update.
6. Press Ctrl + F5.

DISCOUNT MODES
1. No Discount
2. Fixed Amount
   Example: LKR 300 off the complete invoice.
3. Percentage
   Example: 10 means 10% off the subtotal.
4. Per kg / Per Unit
   Example: quantity 2 kg and discount value 300:
   discount = 2 × 300 = LKR 600.

LIVE CALCULATION
Grand Total = Subtotal - Calculated Discount + Tax

SAFETY
- Discount cannot reduce the subtotal below zero.
- Percentage is capped at 100%.
- Server-side calculations remain authoritative.
- Existing v2.8 invoices remain valid and are treated as No Discount unless
  their old discount amount exists.
