feat: update wording (GitHub Stable/Unstable) + billing matrix redesign

Agent-Logs-Url: https://github.com/GameServerPanel/GSP/sessions/4a9c8aab-3782-44a8-a5e4-01b50a813cc0

Co-authored-by: iaretechnician <2749183+iaretechnician@users.noreply.github.com>

modules/billing/add_override_price_column.sql

@@ -0,0 +1,15 @@
+-- Migration: add override_price to billing_service_remote_servers
+-- Run once on existing installs that already have the mapping table (db_version 2)
+-- but are missing the override_price column (added in db_version 3 / module v3.1).
+--
+-- Replace 'gsp_' with your actual table prefix if it differs.
+--
+-- This statement is safe to run multiple times only if your MySQL version supports
+-- ADD COLUMN IF NOT EXISTS (MySQL 8.0.3+).  On older versions, check first:
+--   SHOW COLUMNS FROM gsp_billing_service_remote_servers LIKE 'override_price';
+
+ALTER TABLE `gsp_billing_service_remote_servers`
+    ADD COLUMN IF NOT EXISTS `override_price` DECIMAL(10,2) NULL AFTER `enabled`;
+
+-- If your MySQL is older than 8.0.3, use the conditional form instead:
+-- ALTER TABLE `gsp_billing_service_remote_servers` ADD COLUMN `override_price` DECIMAL(10,2) NULL AFTER `enabled`;