test(drivers): give the Xbox identity a root-enumerated id, and verify the whole thing on Windows

`root\pf_xboxwireless` alongside the plain id, mirroring the DualSense model line — the
INF already documents that variant as the one devgen/devcon tests bind, and without it
the Xbox identity could only be exercised through a running host.

Verified end to end on .173 (Windows 11 26200, WDK 10.0.26100.0):
- build-gamepad-drivers.ps1 builds + signs + catalogs the driver, exit 0
- infverif /v /w on the generated pf_gamepad.inf: "INF is VALID"
- pnputil stages the package; devgen creates the devnode; it starts clean:
  Status OK, Class HIDClass, "Punktfunk Virtual Xbox Wireless Controller"
- it enumerates a HID child, Status OK, carrying HID_DEVICE_SYSTEM_GAME and
  HID_DEVICE_UP:0001_U:0005 — Windows parsed the constructed report descriptor and
  classified the pad as a Game Pad (usage page 0x01, usage 0x05), which is precisely
  what pf-xusb could never do

Test devnode, phantom child, driver package and both certs were removed afterwards.

Two build gotchas worth knowing, both already handled inside build-gamepad-drivers.ps1
and both of which cost a cycle here: CARGO_TARGET_DIR pointing outside the workspace
breaks wdk-sys (wdk-build walks up from OUT_DIR looking for a Cargo.lock and finds
none), and the WDK version must be pinned via Version_Number=10.0.26100.0 or bindgen
picks SDK 10.0.28000.0, which ships no km/crt headers.

Still open: the SwDeviceCreate USB identity (HID\VID_045E&PID_0B13) cannot be checked
through a devgen node, which has no USB hardware ids — that needs the host path. So the
WGI-promotion question is still unanswered, and host routing is still unwritten.

packaging/windows/drivers/pf-gamepad/pf_gamepad.inx

@@ -47,7 +47,7 @@ pf_gamepad.dll=1
 %DeviceDescDS4%=pfGamepad, pf_dualshock4
 %DeviceDescEdge%=pfGamepad, pf_dualsenseedge
 %DeviceDescDeck%=pfGamepad, pf_steamdeck
-%DeviceDescXbox%=pfGamepad, pf_xboxwireless
+%DeviceDescXbox%=pfGamepad, root\pf_xboxwireless, pf_xboxwireless
 
 [pfGamepad.NT]
 CopyFiles=UMDriverCopy