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.

Cargo.lock

@@ -49,14 +49,25 @@ version = "0.1.0"
 name = "contacts-server"
 version = "0.1.0"
 
+[[package]]
+name = "display-qemu"
+version = "0.1.0"
+dependencies = [
+ "display-server",
+ "driver-framebuffer-virtio",
+ "server-framework",
+ "userspace",
+ "userspace-rt",
+]
+
 [[package]]
 name = "display-server"
 version = "0.1.0"
 dependencies = [
+ "driver-framebuffer-mock",
+ "port-framebuffer",
  "server-framework",
  "types",
- "userspace",
- "userspace-rt",
 ]
 
 [[package]]
@@ -66,6 +77,27 @@ dependencies = [
  "types",
 ]
 
+[[package]]
+name = "driver-block-virtio"
+version = "0.1.0"
+dependencies = [
+ "port-block-device",
+]
+
+[[package]]
+name = "driver-framebuffer-mock"
+version = "0.1.0"
+dependencies = [
+ "port-framebuffer",
+]
+
+[[package]]
+name = "driver-framebuffer-virtio"
+version = "0.1.0"
+dependencies = [
+ "port-framebuffer",
+]
+
 [[package]]
 name = "echo"
 version = "0.1.0"
@@ -107,6 +139,7 @@ dependencies = [
 name = "input-server"
 version = "0.1.0"
 dependencies = [
+ "port-input-device",
  "server-framework",
  "types",
  "userspace",
@@ -170,6 +203,18 @@ dependencies = [
  "types",
 ]
 
+[[package]]
+name = "port-block-device"
+version = "0.1.0"
+
+[[package]]
+name = "port-framebuffer"
+version = "0.1.0"
+
+[[package]]
+name = "port-input-device"
+version = "0.1.0"
+
 [[package]]
 name = "power-server"
 version = "0.1.0"
@@ -205,14 +250,23 @@ dependencies = [
  "userspace-rt",
 ]
 
+[[package]]
+name = "storage-qemu"
+version = "0.1.0"
+dependencies = [
+ "storage-server",
+ "userspace-rt",
+]
+
 [[package]]
 name = "storage-server"
 version = "0.1.0"
 dependencies = [
+ "driver-block-virtio",
+ "port-block-device",
  "server-framework",
  "types",
  "userspace",
- "userspace-rt",
 ]
 
 [[package]]