reorg: docs — library/device/ + library/protocol/ structure

Update the docs to match the reorganized tree:

- driver-model.md: the "Families" graph now shows library/device/<domain>/
  (data + logic split) and library/protocol/ instead of the old bus/ + proto/
  sketch; add the microkernel note (the kernel's one library/ import is the
  device-abi data module) and the rule that a driver's hardware command set is
  not a service-seam protocol.
- README.md "Repository layout": device-abi and the protocols move out of
  system/ into library/device/ and library/protocol/; rewrite the "public
  interface as a module" paragraph around the protocol tree and the device
  domains; fix the source-map paths.
- Sweep every remaining stale path reference across docs/ to the moved files.
- Fix vfs-protocol.zig's own header (the standalone VFS server retired; the fat
  server is the backend today).

zig build + test green.

docs/display-plan.md

@@ -39,7 +39,7 @@ initial-ramdisk; protocols are `b.addModule("…-protocol", …)` and imported i
 
 Make the boot framebuffer reachable and mappable **write-combining** from user space.
 
-- [x] [device-abi.zig](../system/devices/device-abi.zig): added `DeviceClass.display`; a
+- [x] [device-abi.zig](../library/device/model/device-abi.zig): added `DeviceClass.display`; a
       `DisplayInfo{ width, height, pitch, format }` carried on the descriptor; a
       `flags` field on `ResourceDescriptor` + `resource_flag_write_combining`.
 - [x] [devices-broker.zig](../system/kernel/devices-broker.zig): `seedDisplay(base, w, h,
@@ -67,7 +67,7 @@ Regression-checked: `discovery`, `ioport`, `claim-release`, `supervision`, `devi
 
 Stand up the named service and the double-buffer, no layers yet.
 
-- [x] `system/services/display/protocol.zig`: `Operation{ info, create_layer,
+- [x] `library/protocol/display/display-protocol.zig`: `Operation{ info, create_layer,
       configure_layer, destroy_layer, fill_rect, blit_tile, damage, present }`; `extern`
       `Request`/`Reply`; size + `maximum_payload` consts. (Model: block/protocol.zig.)
 - [x] [abi.zig](../system/abi.zig): `ServiceId.display = 9`.