release: bump to v6.0.0-alpha.6

Bug Fixes:
- Fix manifestPath error in ide-config-manager causing installation failures
- Fix installer option display to show full labels instead of just values for single/multi-select
- Add conditional documentation installation - users can now opt out of installing docs

Improvements:
- Add install_user_docs configuration option (defaults to true)
- Improve config question display with descriptive labels for better UX
- Update CONTRIBUTING.md to remove references to non-existent 'next' branch

Maintenance:
- Closed 54 legacy v4 issues (older than 1 month) to maintain clean issue tracker

package.json

@@ -1,7 +1,7 @@
 {
   "$schema": "https://json.schemastore.org/package.json",
   "name": "bmad-method",
-  "version": "6.0.0-alpha.5",
+  "version": "6.0.0-alpha.6",
   "description": "Breakthrough Method of Agile AI-driven Development",
   "keywords": [
     "agile",