Preferred monitor: chosen in Optionen > Allgemein, used at the next start

The Internet-Optionen frame becomes Bildschirm with a Monitor dropdown
(Hauptmonitor or a connected monitor, kept by device path in
[display] Monitor=). The borderless window and the render size use that
monitor, falling back to the main monitor when it is not connected.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CMakeLists.txt

@@ -39,6 +39,7 @@ add_library(sacredK SHARED
     src/game/engine/stream.cpp
     src/game/ui/texts.cpp
     src/game/engine/art.cpp
+    src/mods/monitor.cpp
     src/mods/borderless.cpp
     src/mods/widescreen.cpp
     src/mods/hud.cpp