feat: VirtIO keyboard input for QEMU GUI

- Add VirtIO input device driver (device ID 18) reading from eventq
- Translate Linux keycodes (WASD, arrows) to InputEvent
- Kernel probes for VirtIO input device, falls back to UART
- Add -device virtio-keyboard-device to run-gui Makefile target
- input-qemu tries VirtIO first, falls back to UART

Cargo.lock

@@ -114,6 +114,15 @@ dependencies = [
  "port-input-device",
 ]
 
+[[package]]
+name = "driver-input-virtio"
+version = "0.1.0"
+dependencies = [
+ "hw-virtio",
+ "port-input-device",
+ "types",
+]
+
 [[package]]
 name = "echo"
 version = "0.1.0"
@@ -164,6 +173,7 @@ name = "input-qemu"
 version = "0.1.0"
 dependencies = [
  "driver-input-uart",
+ "driver-input-virtio",
  "input-server",
  "server-framework",
  "types",