fix: VirtIO GPU driver and snake rendering through display server

- Fix swapped command IDs: attach_backing was 0x0104 (FLUSH),
  resource_flush was 0x0106 (ATTACH_BACKING). Now correct.
- Increase process stack from 4 pages (16 KB) to 16 pages (64 KB)
  to prevent stack overflow in display process.
- Restructure display-qemu to avoid MockFramebuffer's 32 KB array
  inflating the VirtIO path's stack frame.
- Wire snake app to render through display server via IPC instead
  of UART escape codes. Uses existing renderer.rs pixel renderer.
- Init now delegates display endpoint to snake process.

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

@@ -10,16 +10,29 @@ extern "C" fn main() {
     let ep = CapSlot::const_new(0);
 
     if let Some(fb) = driver_framebuffer_virtio::VirtioFramebuffer::try_new() {
-        let mut srv = display_server::server::DisplayServer::new(fb);
-        server_framework::serve(&mut srv, ep);
+        run_virtio(fb, ep);
     } else {
-        let fb = driver_framebuffer_mock::MockFramebuffer::new(
-            types::display::Dimension::new(640),
-            types::display::Dimension::new(480),
-        );
-        let mut srv = display_server::server::DisplayServer::new(fb);
-        server_framework::serve(&mut srv, ep);
+        run_mock(ep);
     }
 
     loop { userspace::syscall::yield_now(); }
 }
+
+#[inline(never)]
+fn run_virtio(mut fb: driver_framebuffer_virtio::VirtioFramebuffer, ep: CapSlot) {
+    use port_framebuffer::Framebuffer;
+    fb.clear(types::display::Color::rgb(30, 30, 60));
+    fb.flush();
+    let mut srv = display_server::server::DisplayServer::new(fb);
+    server_framework::serve(&mut srv, ep);
+}
+
+#[inline(never)]
+fn run_mock(ep: CapSlot) {
+    let fb = driver_framebuffer_mock::MockFramebuffer::new(
+        types::display::Dimension::new(640),
+        types::display::Dimension::new(480),
+    );
+    let mut srv = display_server::server::DisplayServer::new(fb);
+    server_framework::serve(&mut srv, ep);
+}