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/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "input-qemu"
+version = "0.1.0"
+edition = "2024"
+
+[[bin]]
+name = "input-qemu"
+test = false
+bench = false
+
+[dependencies]
+types = { workspace = true }
+userspace-rt = { workspace = true }
+userspace = { workspace = true }
+server-framework = { workspace = true }
+input-server = { workspace = true }
+driver-input-uart = { workspace = true }