Apache reverse proxy for webapp, UI improvements

- Move Flask to localhost:9010, Apache serves port 9009 with static file
  handling and reverse proxy to fix intermittent asset loading on remote clients
- Add "PXE Manager" branding beneath logo in sidebar
- Increase code editor size (startnet.cmd and unattend XML) to 70vh
- Add test-lab.sh for full lab VM testing

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

webapp/templates/base.html

@@ -55,8 +55,9 @@
       color: #fff;
       border-bottom: 1px solid rgba(255,255,255,0.08);
       display: flex;
+      flex-direction: column;
       align-items: center;
-      gap: 0.5rem;
+      gap: 0.3rem;
     }
     .sidebar .brand .bi {
       font-size: 1.3rem;