Fix npx execution issue with bmad CLI

- Added wrapper script (bmad.js) at root to handle npx execution context
- Fixed module resolution in tools/installer/bin/bmad.js for both local and npx contexts
- Updated package.json bin paths to use the wrapper script
- Handles temporary npx directories properly using execSync

This fixes the issue where `npx github:bmadcode/BMAD-METHOD#v4-alpha bmad`
was dropping into a shell instead of executing the command.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tools/installer/bin/bmad.js

@@ -4,8 +4,28 @@ const { program } = require('commander');
 const inquirer = require('inquirer');
 const chalk = require('chalk');
 const path = require('path');
-const { version } = require('../package.json');
-const installer = require('../lib/installer');
+
+// Handle both execution contexts (from root via npx or from installer directory)
+let version, installer;
+try {
+  // Try installer context first (when run from tools/installer/)
+  version = require('../package.json').version;
+  installer = require('../lib/installer');
+} catch (e) {
+  // Fall back to root context (when run via npx from GitHub)
+  try {
+    version = require('../../../package.json').version;
+    installer = require('../../../tools/installer/lib/installer');
+  } catch (e2) {
+    console.error(chalk.red('Error: Could not load required modules. Please ensure you are running from the correct directory.'));
+    console.error(chalk.yellow('Debug info:'), {
+      __dirname,
+      cwd: process.cwd(),
+      error: e2.message
+    });
+    process.exit(1);
+  }
+}
 
 program
   .version(version)