chore: remove WHM trademark references, rename package, bump v0.4.6

WHM is a registered trademark of cPanel, L.L.C. Replace all occurrences:
- Sidebar: 'Basic WebHost Manager® Setup' → 'Basic NixServer Setup'
- Sidebar: 'WHM Marketplace' → 'NixServer Marketplace'
- Sidebar: 'OpenAPI Documentation for WHM' → 'OpenAPI Documentation for NixServer'
- nixserver/package.json: @nixpanel/whm → @nixpanel/nixserver
- server/src/app.ts: whmDist variable → nixserverDist

package.json

@@ -1,6 +1,6 @@
 {
   "name": "nixpanel-server",
-  "version": "0.4.5",
+  "version": "0.4.6",
   "private": true,
   "workspaces": [
     "server",