Add web management UI, offline packages, WinPE consolidation, and docs

- webapp/: Flask web management app with:
  - Dashboard showing image types and service status
  - USB import page for WinPE deployment content
  - Unattend.xml visual editor (driver paths, specialize commands,
    OOBE settings, first logon commands, raw XML view)
  - API endpoints for services and image management
- SETUP.md: Complete setup documentation for streamlined process
- build-usb.sh: Now copies webapp and optional WinPE images to USB
- playbook: Added webapp deployment (systemd service, Apache reverse
  proxy), offline package verification, WinPE auto-import from USB

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

.gitignore

@@ -26,5 +26,11 @@ offline-packages/
 .DS_Store
 Thumbs.db
 
+# Python
+__pycache__/
+*.pyc
+*.pyo
+venv/
+
 # Secrets
 secrets.md