Add displayinfo.h — cross-platform display enumeration header

src/wg/displayinfo.h

@@ -0,0 +1,24 @@
+#pragma once
+// src/wg/displayinfo.h — Cross-platform display enumeration.
+//
+// C++17 header (no Qt, no Boost).
+// Provides display info for registration with DragonRelay.
+
+#include <string>
+#include <vector>
+
+namespace wg {
+
+struct DisplayInfo {
+    std::string name;        // OS display name (e.g. "\\.\DISPLAY2" on Windows, "HDMI-1" on Linux)
+    std::string friendlyName; // Human-readable (e.g. "Generic PnP Monitor" or same as name)
+    int width;               // Horizontal resolution in pixels
+    int height;              // Vertical resolution in pixels
+    bool isPrimary;          // True if this is the primary display
+};
+
+// Returns all currently connected displays.
+// Returns an empty vector on error (never throws).
+std::vector<DisplayInfo> enumerateDisplays();
+
+} // namespace wg