fix: Add shell: true to npx execSync to prevent permission denied error

The execSync call for 'npx agentvibes@latest install' was failing with
'Permission denied' because the shell was trying to execute 'agentvibes@latest'
directly instead of passing it as an argument to npx.

Adding shell: true ensures the command runs in a proper shell context
where npx can correctly interpret the @latest version syntax.

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

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

tools/cli/commands/install.js

@@ -88,6 +88,7 @@ module.exports = {
             execSync('npx agentvibes@latest install', {
               cwd: result.projectDir,
               stdio: 'inherit',
+              shell: true,
             });
             console.log(chalk.green('\n✓ AgentVibes installation complete'));
           } catch {