refactor: nest Claude Code commands under BMad subdirectory (#307)

- Update installer config to use .claude/commands/BMad/ path
- Modify setupClaudeCode function to create nested directory structure
- Update documentation and upgrader to reflect new command location
- Improves organization by grouping all BMad commands together

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

@@ -558,7 +558,7 @@ class V3ToV4Upgrader {
     try {
       const ideMessages = {
         cursor: "Rules created in .cursor/rules/",
-        "claude-code": "Commands created in .claude/commands/",
+        "claude-code": "Commands created in .claude/commands/BMad/",
         windsurf: "Rules created in .windsurf/rules/",
         trae: "Rules created in.trae/rules/",
         roo: "Custom modes created in .roomodes",