reorg: normalise every protocol alias to its module name

Finish the direct-import convention: a protocol is now aliased to its module
name in snake_case in every file that imports one — consumers and the runtime
client wrappers alike. This kills the last of the alias variety (the generic
`protocol`, plus `power` and `transfer`), so `device_manager_protocol.Hello`
means the same thing everywhere and grepping a module name finds all its uses.

Pure rename (identifier uses only; prose references left untouched via a
guarded pattern). 14 files, 299/299 lines.

zig build + test green; 16 QEMU cases pass (smoke, device-manager,
driver-restart, device-list, pci-scan, usb-hid, usb-storage, display-service,
display-native, display-reattach, input, acpi-ps2, vfs, fat-mount,
power-button, orderly-shutdown).

system/services/crash-test/crash-test.zig

@@ -8,7 +8,7 @@
 
 const std = @import("std");
 const runtime = @import("runtime");
-const protocol = @import("device-manager-protocol");
+const device_manager_protocol = @import("device-manager-protocol");
 
 pub fn main(init: runtime.process.Init) void {
     const argument = init.arguments.get(1) orelse return; // bare: stay silent
@@ -29,8 +29,8 @@ pub fn main(init: runtime.process.Init) void {
         if (manager == null) runtime.system.sleep(20);
     }
     const h = manager orelse return;
-    const hello = protocol.Hello{ .role = @intFromEnum(protocol.Role.device), .device_id = assigned };
-    var reply: [protocol.message_maximum]u8 = undefined;
+    const hello = device_manager_protocol.Hello{ .role = @intFromEnum(device_manager_protocol.Role.device), .device_id = assigned };
+    var reply: [device_manager_protocol.message_maximum]u8 = undefined;
     _ = runtime.ipc.call(h, std.mem.asBytes(&hello), &reply) catch return;
 
     _ = runtime.system.write("crash-test: faulting now\n");