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.

crates/servers/display-server/src/lib.rs

@@ -1,22 +1,8 @@
 #![no_std]
 
-pub mod adapters;
-pub mod framebuffer;
 pub mod protocol;
 pub mod server;
 
 #[cfg(test)]
 #[path = "tests/mod.rs"]
 mod tests;
-
-pub fn run() -> ! {
-    #[cfg(feature = "qemu-virt")]
-    let fb = adapters::qemu_virtio::VirtioFramebuffer::new(0x10008000);
-
-    #[cfg(not(feature = "qemu-virt"))]
-    let fb = adapters::mock::MockFramebuffer::new(320, 240);
-
-    let mut srv = server::DisplayServer::new(fb);
-    server_framework::serve(&mut srv, 0);
-    loop { userspace::syscall::yield_now(); }
-}