fix: update installer package.json version to 5.1.0

- Fixes version reporting in npx bmad-method --version
- Ensures installer displays correct version number

tools/installer/package.json

@@ -1,6 +1,6 @@
 {
   "name": "bmad-method",
-  "version": "5.0.0",
+  "version": "5.1.0",
   "description": "BMad Method installer - AI-powered Agile development framework",
   "keywords": [
     "bmad",