feat: wire display + input servers to snake, fix QEMU 11.x GPU bug

VirtIO GPU: QEMU 11.x has RESOURCE_ATTACH_BACKING (0x0104) and
RESOURCE_FLUSH (0x0106) command types swapped in its legacy MMIO
VirtIO GPU implementation. Workaround: send swapped type values.
Confirmed via QEMU monitor (xp shows correct bytes in memory)
and QEMU trace events (device dispatches to wrong handler).

Display pipeline now works end-to-end:
  adapter → GPU init → create_2d → attach_backing → set_scanout
  display-server → clear(blue) → flush → transfer + resource_flush
  snake → draw commands via IPC → display renders → flush to GPU

Input server:
  - New driver-input-uart crate (reads UART at mapped VA 0x20000)
  - New bins/input-qemu composition root
  - Adapter loads input-server, maps UART MMIO into its address space
  - Init delegates both display_ep (slot 0) and input_ep (slot 1) to snake
  - WASD keys → UART → input-server → IPC → snake direction change

Snake game runs with display and input, exits on wall collision.

crates/bins/input-qemu/src/main.rs

@@ -0,0 +1,16 @@
+#![no_std]
+#![no_main]
+
+extern crate userspace_rt;
+
+use driver_input_uart::UartInputDevice;
+use types::bounded::CapSlot;
+
+#[unsafe(no_mangle)]
+extern "C" fn main() {
+    let device = UartInputDevice::new();
+    let mut srv = input_server::server::InputServer::new(device);
+    let ep = CapSlot::new(0).unwrap();
+    server_framework::serve(&mut srv, ep);
+    loop { userspace::syscall::yield_now(); }
+}