reorg: move device data modules into library/device/<domain>/

First step of the device-code reorganization (plan: group device code by
domain, split each domain into a shareable data module + a logic module).
This moves the pure-data modules — the enums, wire types, and taxonomies
that any layer including the kernel can import cheaply — out of
system/devices/ and into their domain home:

  device-abi  -> library/device/model/device-abi.zig
  pci-class   -> library/device/pci/pci-class.zig
  usb-abi     -> library/device/usb/usb-abi.zig
  usb-ids     -> library/device/usb/usb-ids.zig
  acpi-ids    -> library/device/acpi/acpi-ids.zig
  aml/        -> library/device/acpi/aml/

Module names are unchanged, so this is a pure file move: only the
b.addModule paths and the host-test file list in build.zig change; no
importer is touched. system/devices/ now holds only the kernel-internal
device model (device-model, platform, acpi, device-tree, power).

The device *logic* (the pci Function helper, the usb transfer client) and
the kernel's cosmetic taxonomy dependency are handled in following commits.

zig build + zig build test green.

build.zig

@@ -280,12 +280,12 @@ pub fn build(b: *std.Build) void {
     // its own module like vfs-protocol — importable by user space, unlike the
     // kernel-internal device model it also feeds (system/devices/device-model.zig).
     const device_abi_module = b.addModule("device-abi", .{
-        .root_source_file = b.path("system/devices/device-abi.zig"),
+        .root_source_file = b.path("library/device/model/device-abi.zig"),
     });
     // PCI class-code decoding (class/subclass/prog-IF -> names). Pure reference data,
     // shared by kernel discovery (the device-tree dump) and any user-space PCI tool.
     const pci_class_module = b.addModule("pci-class", .{
-        .root_source_file = b.path("system/devices/pci-class.zig"),
+        .root_source_file = b.path("library/device/pci/pci-class.zig"),
     });
     // ACPI/PnP hardware-ID (_HID) names — the flat analog of pci-class for acpi_device
     // nodes. Also shared reference data.
@@ -293,11 +293,11 @@ pub fn build(b: *std.Build) void {
     // same parser the kernel does (docs/discovery.md — the shared AML module).
     // Pure Zig, no kernel imports — one source, two builds.
     const aml_module = b.addModule("aml", .{
-        .root_source_file = b.path("system/devices/aml/aml.zig"),
+        .root_source_file = b.path("library/device/acpi/aml/aml.zig"),
     });
 
     const acpi_ids_module = b.addModule("acpi-ids", .{
-        .root_source_file = b.path("system/devices/acpi-ids.zig"),
+        .root_source_file = b.path("library/device/acpi/acpi-ids.zig"),
     });
 
     // The USB device-framework wire ABI (chapter-9 set-up packets, standard +
@@ -305,10 +305,10 @@ pub fn build(b: *std.Build) void {
     // reference the xHCI bus driver, the USB class drivers, and the device
     // manager's identity matcher all share. Pure data, like pci-class/acpi-ids.
     const usb_abi_module = b.addModule("usb-abi", .{
-        .root_source_file = b.path("system/devices/usb-abi.zig"),
+        .root_source_file = b.path("library/device/usb/usb-abi.zig"),
     });
     const usb_ids_module = b.addModule("usb-ids", .{
-        .root_source_file = b.path("system/devices/usb-ids.zig"),
+        .root_source_file = b.path("library/device/usb/usb-ids.zig"),
     });
     // The USB transfer protocol: what a USB class driver says to the xHCI bus
     // driver to drive its device (open / control / interrupt / bulk). A protocol
@@ -919,12 +919,12 @@ pub fn build(b: *std.Build) void {
         "system/boot-handoff.zig",
         "system/abi.zig",
         "system/initial-ramdisk.zig", // v2 path-named entries: find/basename/magic
-        "system/devices/device-abi.zig",
+        "library/device/model/device-abi.zig",
-        "system/devices/pci-class.zig", // class/subclass/prog-IF name decoding
+        "library/device/pci/pci-class.zig", // class/subclass/prog-IF name decoding
-        "system/devices/acpi-ids.zig", // _HID name decoding
+        "library/device/acpi/acpi-ids.zig", // _HID name decoding
-        "system/devices/aml/aml.zig", // AML parse + interpret, incl. Notify dispatch (M21)
+        "library/device/acpi/aml/aml.zig", // AML parse + interpret, incl. Notify dispatch (M21)
-        "system/devices/usb-abi.zig", // wire sizes + bit packings + set-up packet encodings
+        "library/device/usb/usb-abi.zig", // wire sizes + bit packings + set-up packet encodings
-        "system/devices/usb-ids.zig", // class/subclass/protocol code assignments
+        "library/device/usb/usb-ids.zig", // class/subclass/protocol code assignments
         "library/mmio/mmio.zig", // barriers assemble + registers round-trip
         "system/drivers/ps2-bus/scancode.zig", // set-2 decode + keyboard state machine
         "system/drivers/ps2-bus/mouse-packet.zig", // 3-byte mouse packet assembly