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).

library/runtime/block.zig

@@ -10,7 +10,7 @@
 const std = @import("std");
 const ipc = @import("ipc.zig");
 const system = @import("system.zig");
-const protocol = @import("block-protocol");
+const block_protocol = @import("block-protocol");
 
 pub const Geometry = struct { block_size: u32, block_count: u64 };
 
@@ -19,11 +19,11 @@ pub const Device = struct {
 
     /// The device's block size and total block count.
     pub fn geometry(self: Device) ?Geometry {
-        var request = protocol.Request{ .operation = @intFromEnum(protocol.Operation.geometry), .lba = 0, .count = 0, .physical = 0 };
-        var reply: [protocol.reply_size]u8 = undefined;
+        var request = block_protocol.Request{ .operation = @intFromEnum(block_protocol.Operation.geometry), .lba = 0, .count = 0, .physical = 0 };
+        var reply: [block_protocol.reply_size]u8 = undefined;
         const n = ipc.call(self.endpoint, std.mem.asBytes(&request), &reply) catch return null;
-        if (n < protocol.reply_size) return null;
-        const result = std.mem.bytesToValue(protocol.Reply, reply[0..protocol.reply_size]);
+        if (n < block_protocol.reply_size) return null;
+        const result = std.mem.bytesToValue(block_protocol.Reply, reply[0..block_protocol.reply_size]);
         if (result.status != 0) return null;
         return .{ .block_size = result.block_size, .block_count = result.block_count };
     }
@@ -45,12 +45,12 @@ pub const Device = struct {
         return self.transfer(.flush, 0, 0, 0);
     }
 
-    fn transfer(self: Device, operation: protocol.Operation, lba: u64, count: u32, physical: u64) bool {
-        var request = protocol.Request{ .operation = @intFromEnum(operation), .lba = lba, .count = count, .physical = physical };
-        var reply: [protocol.reply_size]u8 = undefined;
+    fn transfer(self: Device, operation: block_protocol.Operation, lba: u64, count: u32, physical: u64) bool {
+        var request = block_protocol.Request{ .operation = @intFromEnum(operation), .lba = lba, .count = count, .physical = physical };
+        var reply: [block_protocol.reply_size]u8 = undefined;
         const n = ipc.call(self.endpoint, std.mem.asBytes(&request), &reply) catch return false;
-        if (n < protocol.reply_size) return false;
-        return std.mem.bytesToValue(protocol.Reply, reply[0..protocol.reply_size]).status == 0;
+        if (n < block_protocol.reply_size) return false;
+        return std.mem.bytesToValue(block_protocol.Reply, reply[0..block_protocol.reply_size]).status == 0;
     }
 };