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/installer/config/install.config.yaml

@@ -21,7 +21,7 @@ ide-configurations:
       # 3. The agent will adopt that persona for the conversation
   claude-code:
     name: Claude Code
-    rule-dir: .claude/commands/
+    rule-dir: .claude/commands/BMad/
     format: multi-file
     command-suffix: .md
     instructions: |

tools/installer/lib/ide-setup.js

@@ -131,7 +131,7 @@ class IdeSetup {
   }
 
   async setupClaudeCode(installDir, selectedAgent) {
-    const commandsDir = path.join(installDir, ".claude", "commands");
+    const commandsDir = path.join(installDir, ".claude", "commands", "BMad");
     const agents = selectedAgent ? [selectedAgent] : await this.getAllAgentIds(installDir);
 
     await fileManager.ensureDirectory(commandsDir);