Report Valve (Steam) controllers as Xbox type to the host

SDL has no gamepad type for Steam Controllers, so they arrived as
LI_CTYPE_UNKNOWN with gyro/accel/touchpad capabilities and Sunshine's
auto mode emulated a DualShock. Report LI_CTYPE_XBOX for vendor 0x28de
so the host emulates an X360 pad matching the controller's layout.

Author: Drackrath

app/streaming/input/gamepad.cpp

@@ -701,7 +701,20 @@ void SdlInputHandler::handleControllerDeviceEvent(SDL_ControllerDeviceEvent* eve
             type = LI_CTYPE_NINTENDO;
             break;
         default:
-            type = LI_CTYPE_UNKNOWN;
+            // SDL has no gamepad type for Valve's Steam Controllers (the 2nd-gen
+            // 2026 model and its Proteus/Nereid wireless dongle included), so they
+            // land here as UNKNOWN while still advertising gyro/accel/touchpad
+            // capabilities. Sunshine's "auto" gamepad selection treats an unknown
+            // pad with motion/touchpad caps as a DualShock and emulates a PS
+            // controller on the host. The Steam Controller has an Xbox-style
+            // layout (ABXY, Menu/View, analog triggers), so tell the host it's an
+            // Xbox pad and let it emulate an X360/XInput device instead.
+            if (vendorId == 0x28de) {
+                type = LI_CTYPE_XBOX;
+            }
+            else {
+                type = LI_CTYPE_UNKNOWN;
+            }
             break;
         }