fix: add default current directory to installer prompt

Previously users had to manually type the full path or run pwd to get
the current directory when installing BMad. Now the installer prefills
the current working directory as the default, improving UX.

tools/installer/bin/bmad.js

@@ -216,6 +216,7 @@ async function promptInstallation() {
       type: 'input',
       name: 'directory',
       message: 'Enter the full path to your project directory where BMad should be installed:',
+      default: process.cwd(),
       validate: (input) => {
         if (!input.trim()) {
           return 'Please enter a valid project path';