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/installer/lib/ide-setup.js

@@ -68,7 +68,7 @@ class IdeSetup extends BaseIdeSetup {
   }
 
   async setupCursor(installDir, selectedAgent) {
-    const cursorRulesDir = path.join(installDir, ".cursor", "rules");
+    const cursorRulesDir = path.join(installDir, ".cursor", "rules", "bmad");
     const agents = selectedAgent ? [selectedAgent] : await this.getAllAgentIds(installDir);
 
     await fileManager.ensureDirectory(cursorRulesDir);