fix: resolve Windows compatibility issues in compile-js plugin

[idpcks]

Problem

When initializing the boilerplate on Windows, the post-init script
fails with spawnSync yarn ENOENT error.

Root Cause

1. execSync and spawnSync calls missing shell: true option,
   causing Windows to fail resolving PATH for yarn/npm binaries.
2. Unix commands (cp, rm -rf) are not available on Windows
   Command Prompt.

Fix

1. Added shell: true to all execSync and spawnSync calls.
2. Replaced Unix commands with Node.js native fs.cpSync and
   fs.rmSync for cross-platform compatibility.

Tested on

• Windows 11
• Node.js v22.13.1
• npm (without yarn installed)