Phase 1 (3b): driver signing/install scripts + C# HID feeder sink

Make the virtual gamepad deployable on owned cabinets and wire the real
user-mode feeder:

- driver/sign.ps1 (non-admin): create a self-signed code-signing cert, build the
  catalog with inf2cat, and SHA-256-sign RioGamepad.sys + .cat (embed-sign the sys
  before cataloguing so the .cat matches). Exports RIOJoyTest.cer. Verified
  end-to-end against the EWDK (signability + catalog clean; both files signed).
- driver/install.ps1 (admin, two-phase): trust the cert (LocalMachine Root +
  TrustedPublisher), stage the package (pnputil /add-driver), enable test signing;
  after reboot, -CreateDevice runs devgen to create root\RioGamepad so PnP installs
  it. uninstall.ps1 reverses it.
- RioJoy.Core.Output.HidFeederJoystickSink: opens the driver by
  GUID_DEVINTERFACE_RIOGAMEPAD (SetupAPI), maintains a RioHidReport, and submits it
  via DeviceIoControl(IOCTL_RIO_SUBMIT_REPORT) on each axis/button/hat change.
  RioCoordinator now uses it when the driver is present and falls back to the no-op
  sink otherwise (status shows "[no joystick driver]").
- gitignore the signing outputs (driver/package/, *.cat); driver/README.md gets the
  full build → sign → install → joy.cpl workflow.

Remaining = the actual elevated install + reboot + joy.cpl verification on the
cabinet (admin steps), and on-hardware confirmation of the feeder.

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

.gitignore

@@ -366,7 +366,9 @@ FodyWeavers.xsd
 ###############################################################################
 # WDK / driver build outputs
 [Dd]river/**/[Xx]64/
+[Dd]river/package/
 *.cer
+*.cat
 *.pvk
 # Local run-time config that shouldn't be versioned
 *.local.json