add enableRDP flag to generalize and fix AutoLogon

- generalize.nix: add enableRDP option that re-enables RDP in
  post-oobe.cmd after sysprep resets registry (firewall rules,
  TermService auto-start, disable NLA)
- Fix OOBE AutoLogon: create user with blank password (Windows
  ignores unattend passwords), set real password via net user in
  post-oobe.cmd, and explicitly set AutoAdminLogon registry values
- Add LogonCount=999 for persistent AutoLogon across reboots
- Remove unused rdpEntries import from registry/default.nix

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/images/windows/templates/registry/default.nix

@@ -9,7 +9,6 @@ let
     ${entries}
   '';
 
-  rdpEntries = import ./rdp.nix;
   telemetryEntries = import ./telemetry.nix;
   errorReportingEntries = import ./error-reporting.nix;
   defenderEntries = import ./defender.nix;