feat(gamepad): pure-user-mode Windows DualShock 4 + Xbox 360 (drop ViGEm) + installer + multi-pad

Windows virtual gamepads now have zero external dependencies - ViGEmBus is removed.

- DualShock 4: Windows UMDF backend (inject/dualshock4_windows.rs + dualshock4_proto.rs),
  reusing the DualSense SwDeviceCreate game-detection identity fix. The one UMDF driver serves
  the DS5 or DS4 identity/descriptor/features/strings per a device_type byte the host stamps into
  shared memory. Driver also gains IOCTL_HID_GET_STRING and a 41-byte calibration feature.
- Xbox 360: a new UMDF2 XUSB companion driver (packaging/windows/xusb-driver/) that registers
  GUID_DEVINTERFACE_XUSB and answers the buffered XInput IOCTLs from a shared section, so classic
  XInputGetState/SetState work with no kernel bus driver. inject/gamepad_windows.rs is rewritten
  to drive it and the vigem-client dependency is removed. Xbox One folds to the 360 XInput path.
- Installer: vendor + pnputil-install the three UMDF drivers (packaging/windows/gamepad-drivers/
  + install-gamepad-drivers.ps1, wired into pack-host-installer.ps1 + punktfunk-host.iss).
- Multi-pad: the host stamps each pad index into the device Location (pszDeviceLocation); the
  driver reads it via WdfDeviceAllocAndQueryProperty to map its own *-shm-<index>, with
  UmdfHostProcessSharing=ProcessSharingDisabled giving each pad its own host (per-pad statics).

Validated live on the Windows host: Cyberpunk native DualSense detection, DS4 identity + descriptor,
XInputGetState + rumble round-trip, two pads -> two distinct XInput slots, and a full installer build.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/windows/pack-host-installer.ps1

@@ -147,6 +147,23 @@ if (-not $NoDriver) {
 }
 else { Write-Host "-NoDriver: building installer WITHOUT the bundled SudoVDA driver" }
 
+# --- stage the punktfunk virtual-gamepad UMDF drivers (DualSense/DS4 + Xbox 360 XUSB) ----------
+# Vendored, pre-signed under packaging/windows/gamepad-drivers/ (like SudoVDA). Rebuild + re-vendor
+# from packaging/windows/{dualsense,xusb}-driver/ when the driver source changes (see their READMEs).
+if (-not $NoDriver) {
+    $gpVendor = Join-Path $here 'gamepad-drivers'
+    if (Test-Path (Join-Path $gpVendor 'pf_dualsense.inf')) {
+        $gpStage = Join-Path $OutDir 'gamepad'
+        if (Test-Path $gpStage) { Remove-Item -Recurse -Force $gpStage }
+        New-Item -ItemType Directory -Force -Path $gpStage | Out-Null
+        Copy-Item (Join-Path $gpVendor '*') $gpStage -Force
+        Copy-Item (Join-Path $here 'install-gamepad-drivers.ps1') (Join-Path $gpStage 'install-gamepad-drivers.ps1') -Force
+        $defines += "/DGamepadStageDir=$gpStage"
+        Write-Host "==> staged vendored gamepad UMDF drivers from $gpVendor"
+    }
+    else { Write-Warning "no vendored gamepad drivers under $gpVendor — installer built WITHOUT them" }
+}
+
 # --- stage the FFmpeg shared DLLs (AMD/Intel AMF/QSV build) ------------------------------------
 # A host built with --features amf-qsv link-imports avcodec/avutil/swscale/... so the shared DLLs
 # MUST sit next to the exe (it won't start otherwise). Bundle them from $FfmpegDir\bin — the same