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/apps/snake/Cargo.toml

@@ -12,3 +12,5 @@ bench = false
 types = { workspace = true }
 userspace = { workspace = true }
 userspace-rt = { workspace = true }
+display-server = { workspace = true }
+server-framework = { workspace = true }