chore: bump version to 6.0.0-alpha.18

Major improvements:
- BMGD module complete overhaul with professional game development workflows
- New Game QA (GLaDOS) and Game Solo Dev (Indie) agents
- 15 comprehensive testing guides for all major game engines
- Agent recompile feature for quick updates without full reinstall
- Full agent customization support - ALL fields now customizable
- Enhanced custom module installation and management
- Complete BMGD documentation suite with 9 guides

package.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/package.json",
   "name": "bmad-method",
-  "version": "6.0.0-alpha.17",
+  "version": "6.0.0-alpha.18",
   "description": "Breakthrough Method of Agile AI-driven Development",
   "keywords": [
     "agile",