feat: rename WHM→NixServer, cPanel→NixClient, bump v0.2.0

- Rename frontend workspaces: whm/ → nixserver/, cpanel/ → nixclient/
- Rename server route dirs: routes/whm/ → routes/nixserver/, routes/cpanel/ → routes/nixclient/
- Update all API prefixes: /api/whm → /api/nixserver, /api/cpanel → /api/nixclient
- Rename env vars: WHM_PORT → NIXSERVER_PORT, CPANEL_PORT → NIXCLIENT_PORT
- Update config properties: whmPort → nixserverPort, cpanelPort → nixclientPort
- Update all UI labels, login pages, sidebar branding, and error messages
- Update installer and update scripts to match new names
- Add cpanel email route (missing from initial scaffold)
- Add .gitattributes to enforce LF line endings
- Bump version to 0.2.0 across all package.json files

nixserver/src/main.tsx

@@ -0,0 +1,10 @@
+import React from 'react'
+import ReactDOM from 'react-dom/client'
+import App from './App'
+import './index.css'
+
+ReactDOM.createRoot(document.getElementById('root')!).render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>
+)