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

crates/drivers/input/virtio/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "driver-input-virtio"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+port-input-device = { workspace = true }
+hw-virtio = { workspace = true }
+types = { workspace = true }