Phase 8B: RioGamepadXP.sys — WDM HID minidriver for Windows XP

The XP flavor of our own virtual joystick (no third-party driver), built
with WDK 7.1.0 to x86/subsystem-5.01. Exposes the identical Public.h
contract as the modern KMDF+VHF driver — same GUID, IOCTL_RIO_SUBMIT_REPORT,
25-byte report, VID/PID — so HidFeederJoystickSink drives both.

Design (driver/RioGamepadXP/rioxp.c):
- WDM HID minidriver via HidRegisterMinidriver presenting the 6-axis/hat/
  96-button joystick. POLLED mode (DevicesArePolled=TRUE): hidclass paces
  IOCTL_HID_READ_REPORT and we complete each synchronously from a cached
  report — no pending-IRP or cancel-routine machinery (the usual crash
  surface in a virtual HID driver).
- Named sideband control device (\Device\RioGamepadXP + \DosDevices symlink)
  takes IOCTL_RIO_SUBMIT_REPORT and updates the cache under a spinlock.
- hidclass overwrites our CREATE/CLOSE/DEVICE_CONTROL during registration;
  we save its pointers and reinstall wrappers that route the control device's
  IRPs to us and forward the HID FDO's to hidclass.

Packaging/install:
- Root-enumerated, so install uses devcon (built from the same WDK) —
  InstallHinfSection can't create the devnode. install-core.bat runs
  "devcon install RioGamepadXP.inf root\RioGamepadXP"; unsigned is fine
  (XP x86 enforces no kernel signing). Bundled into vendor\xp\.
- net40 feeder opens the driver by name (\.\RioGamepadXP); XP can't put a
  device interface on a bare control device (no PDO) — the one nuance.

Static build only: compiles clean but runtime bring-up (joy.cpl enumeration,
report flow) needs a real XP target — that's 8E. 275 tests still green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/RioJoy.Core/Output/HidFeederJoystickSink.cs

@@ -36,7 +36,15 @@ public sealed class HidFeederJoystickSink : IJoystickSink, IDisposable
     public static bool TryCreate(out HidFeederJoystickSink? sink)
     {
         sink = null;
+#if NET40
+        // Windows XP: RioGamepadXP is a HID minidriver whose sideband control
+        // device can't carry a device interface (no PDO), so it's opened by its
+        // fixed symbolic-link name rather than via SetupDi + interface GUID.
+        // Contract is otherwise identical (see driver/RioGamepadXP/Public.h).
+        string? path = @"\\.\RioGamepadXP";
+#else
         string? path = FindDevicePath();
+#endif
         if (path is null)
             return false;