refactor: extract ports/drivers/bins layers — clean dependency inversion

Separate abstractions from implementations following DIP:

  servers/              drivers/
      │                     │
      ▼                     ▼
    ports/  (trait-only crates, zero deps)

New crates:

ports/ (abstractions):
  - port-framebuffer: Framebuffer trait
  - port-block-device: BlockDevice trait + SectorId
  - port-input-device: InputDevice trait + InputEvent types

drivers/ (implementations depend on ports/):
  - driver-framebuffer-virtio: VirtIO GPU framebuffer
  - driver-framebuffer-mock: test double
  - driver-block-virtio: VirtIO block device

bins/ (composition roots wire server + driver):
  - display-qemu: DisplayServer<VirtioFramebuffer>
  - storage-qemu: storage server with VirtIO block

Servers no longer own their hardware traits or driver code.
Neither server nor driver depends on the other — both point
inward to the port abstraction.

scripts/make-disk-image.sh

@@ -24,11 +24,11 @@ copy() {
 copy init       "init.elf"
 copy echo       "echo.elf"
 copy snake      "snake.elf"
-copy display-server "display.elf"
+copy display-qemu   "display.elf"
 copy input-server   "input.elf"
 copy log-server     "log.elf"
 copy permission-manager "permis.elf"
-copy storage-server "storage.elf"
+copy storage-qemu   "storage.elf"
 copy session-server "session.elf"
 
 echo ""