reorg: begin library/protocol/ — move block + usb-transfer

Start the protocol tree: wire protocols move to library/protocol/<name>/,
entry file <name>-protocol.zig, module name unchanged. block and usb-transfer
are pure moves — every consumer already imports them by module name, so only
the b.addModule paths change and the empty system/services/block/ is removed.

  block-protocol         -> library/protocol/block/block-protocol.zig
  usb-transfer-protocol  -> library/protocol/usb-transfer/usb-transfer-protocol.zig

zig build + test green.

system/services/block/protocol.zig

@@ -1,44 +0,0 @@
-//! The block-device wire protocol — what a filesystem (the FAT server) says to a
-//! block driver (usb-storage) over its well-known `.block` endpoint. A protocol
-//! module like vfs-protocol / usb-transfer-protocol: extern-struct messages, an
-//! `Operation` tag, everything in one IPC message.
-//!
-//! Data path: read and write move whole blocks to or from a **caller-owned DMA
-//! buffer**, named by its physical address — the same physical-address handoff
-//! usb-storage already uses toward the controller, one layer up. So a 512-byte
-//! sector never has to cross the 256-byte IPC boundary; only the small request /
-//! reply headers do. (Safe while the IOMMU is unenforced; see docs/driver-model.md.)
-
-pub const Operation = enum(u32) {
-    /// geometry() -> { block_size, block_count }
-    geometry = 0,
-    /// read(lba, count, physical): read `count` blocks from `lba` into the buffer
-    read = 1,
-    /// write(lba, count, physical): write `count` blocks at `lba` from the buffer
-    write = 2,
-    /// flush(): commit any device write cache to stable media (no data transfer).
-    /// A filesystem calls this to make prior writes durable — e.g. before power-off,
-    /// so a shutdown-time write isn't lost in the USB flash controller's cache.
-    flush = 3,
-};
-
-pub const Request = extern struct {
-    operation: u32,
-    reserved: u32 = 0,
-    lba: u64,
-    count: u32, // number of blocks (read/write)
-    reserved2: u32 = 0,
-    physical: u64, // caller's DMA buffer physical address (read/write)
-};
-
-pub const Reply = extern struct {
-    status: i32, // 0 on success, negative on failure
-    reserved: u32 = 0,
-    block_size: u32, // geometry: bytes per block (512)
-    reserved2: u32 = 0,
-    block_count: u64, // geometry: total blocks; read/write: blocks moved
-};
-
-pub const message_maximum: usize = 256;
-pub const request_size: usize = @sizeOf(Request);
-pub const reply_size: usize = @sizeOf(Reply);

system/services/device-manager/device-manager.zig

@@ -42,6 +42,13 @@ const virtio_gpu_pci_class: u64 = pci_class.ClassCode.pack(.{
     .prog_if = 0,
 });
 
+
+const vga_compatible_gpu_pci_class: u64 = pci_class.ClassCode.pack(.{
+    .base = @intFromEnum(pci_class.BaseClass.display),
+    .subclass = @intFromEnum(pci_class.display.SubClass.vga_compatible),
+    .prog_if = 0,
+});
+
 /// The driver that serves a *reported* PCI function (M19.3: matching moved
 /// from the boot snapshot to the bus reports), or null. A machine can carry
 /// several identical controllers — one driver instance per reported device,
@@ -49,6 +56,7 @@ const virtio_gpu_pci_class: u64 = pci_class.ClassCode.pack(.{
 fn pciDriverForIdentity(identity: u64) ?[]const u8 {
     return switch (identity) {
         xhci_pci_class => "/system/drivers/usb-xhci-bus",
+        vga_compatible_gpu_pci_class => "/system/drivers/display",
         virtio_gpu_pci_class => "/system/drivers/virtio-gpu",
         else => null,
     };