feat: install Cursor rules to subdirectory (#438)

* feat: install Cursor rules to subdirectory

Implement feature request #376 to avoid filename collisions and confusion
between repo-specific and BMAD-specific rules.

Changes:
- Move Cursor rules from .cursor/rules/ to .cursor/rules/bmad/
- Update installer configuration to use new subdirectory structure
- Update upgrader to reflect new rule directory path

This keeps BMAD Method files separate from existing project rules,
reducing chance of conflicts and improving organization.

Fixes #376

* chore: correct formatting in cursor rules directory path

---------

Co-authored-by: Stefan Klümpers <stefan.kluempers@materna.group>

tools/upgraders/v3-to-v4-upgrader.js

@@ -557,7 +557,7 @@ class V3ToV4Upgrader {
 
     try {
       const ideMessages = {
-        cursor: "Rules created in .cursor/rules/",
+        cursor: "Rules created in .cursor/rules/bmad/",
         "claude-code": "Commands created in .claude/commands/BMad/",
         windsurf: "Rules created in .windsurf/rules/",
         trae: "Rules created in.trae/rules/",