fix: GPU display at correct resolution, clean up diagnostics

- Add GET_DISPLAY_INFO command to query QEMU's preferred resolution
  (was hardcoded 640x480, QEMU wanted 1280x800)
- Allocate framebuffer matching actual display dimensions
- Remove debug diagnostic output from display server and snake

crates/hw-virtio/src/gpu.rs

@@ -83,6 +83,24 @@ fn write_cmd_header(cmd_va: VirtualAddress, cmd_type: u32) {
     }
 }
 
+pub fn get_display_info(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs) -> Option<(u32, u32)> {
+    write_cmd_header(dma.cmd_va, 0x0100);
+    let descs = [
+        Descriptor { addr: dma.cmd_pa.raw() as u64, len: 24, writable: false },
+        Descriptor { addr: dma.resp_pa.raw() as u64, len: 408, writable: true },
+    ];
+    if !queue.submit(mmio, &descs) { return None; }
+    unsafe {
+        let resp = dma.resp_pa.raw() as usize;
+        let resp_va = dma.cmd_va.raw() + 512;
+        let resp_type = core::ptr::read_volatile(resp_va as *const u32);
+        if resp_type != 0x1101 { return None; }
+        let w = core::ptr::read_volatile((resp_va + 24 + 8) as *const u32);
+        let h = core::ptr::read_volatile((resp_va + 24 + 12) as *const u32);
+        if w > 0 && h > 0 { Some((w, h)) } else { None }
+    }
+}
+
 fn submit_cmd(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, cmd_len: u32) -> bool {
     let descs = [
         Descriptor { addr: dma.cmd_pa.raw() as u64, len: cmd_len, writable: false },