feat: update license terms to clarify commercial use restrictions

Author: ductridev

LICENSE

@@ -1,9 +1,13 @@
 BUNGO MULTI-DISCORD BOTS - CUSTOM LICENSE
+SPDX-License-Identifier: LicenseRef-BungoMusic-1.0
 Version 1.0, January 2025
 
 Copyright (c) 2025 ductridev
 All rights reserved.
 
+This is a proprietary source-available license with commercial restrictions.
+Public and commercial use requires a separate paid license.
+
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 TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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