reorg: move power-protocol to library/protocol; finish the protocol tree

power-protocol -> library/protocol/power/power-protocol.zig. Its two consumers
(init and the acpi discovery service) import it directly; the
runtime.power_protocol re-export and the runtime module import are dropped (no
runtime client speaks it). The now-empty system/services/power/ is removed.

This completes library/protocol/: every driver<->service wire contract lives
there and is imported by module name, no protocol is re-exported through
runtime, and the alias chaos (dp/sp, mixed protocol/<x>_protocol) is resolved.
virtio-gpu-protocol stays a driver-private relative import (a hardware command
set, not a driver<->service seam — like virtio-pci.zig beside it).

zig build + test green; power-button, orderly-shutdown pass.

build.zig

@@ -420,11 +420,11 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("library/protocol/scanout/scanout-protocol.zig"),
     });
 
-    // The power protocol: system power's domain-named surface (docs/power.md).
+    // The power protocol: system power's domain-named surface (docs/power.md). No runtime
+    // client speaks it — imported directly by init and the acpi discovery service.
     const power_protocol_module = b.addModule("power-protocol", .{
-        .root_source_file = b.path("system/services/power/protocol.zig"),
+        .root_source_file = b.path("library/protocol/power/power-protocol.zig"),
     });
-    runtime_module.addImport("power-protocol", power_protocol_module);
 
     // Typed volatile MMIO register access + memory-ordering barriers, for drivers on
     // top of an mmio_map grant. Depends only on `builtin` (arch-conditional barriers);
@@ -530,6 +530,7 @@ pub fn build(b: *std.Build) void {
     // linked into the kernel's user region against the `runtime` runtime library, and
     // started in ring 3 by the kernel's user-ELF loader.
     const init_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "init", "system/services/init/init.zig");
+    programModule(init_exe).addImport("power-protocol", power_protocol_module);
     // init reads the same `serial` flag the kernel does: its liveness heartbeat is a
     // serial/test-build diagnostic (the QEMU harness's init tests assert on it, and
     // -Dserial images emit it), so a flashable image runs a purely event-driven PID 1
@@ -618,6 +619,7 @@ pub fn build(b: *std.Build) void {
     const discovery_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "discovery", discovery_source);
     if (discovery == .acpi) programModule(discovery_exe).addImport("aml", aml_module);
     if (discovery == .acpi) programModule(discovery_exe).addImport("device-manager-protocol", device_manager_protocol_module);
+    if (discovery == .acpi) programModule(discovery_exe).addImport("power-protocol", power_protocol_module);
     const device_manager_exe = addUserBinary(b, kernel_target, runtime_module, mmio_module, xkeyboard_config_module, acpi_ids_module, "device-manager", "system/services/device-manager/device-manager.zig");
     // Names the xHCI PCI class triple from the shared taxonomy instead of a bare 0x0C0330.
     programModule(device_manager_exe).addImport("pci-class", pci_class_module);

library/runtime/runtime.zig

@@ -24,9 +24,6 @@ pub const start = @import("start.zig");
 /// protocol itself is the library/protocol/device-manager module, imported
 /// directly by drivers and services that speak it.
 pub const device_manager = @import("device-manager.zig");
-
-/// The power protocol: events (button, lid, battery) + shutdown (docs/power.md).
-pub const power_protocol = @import("power-protocol");
 /// Keyboard-event listening (subscribe/next) and broadcasting (publish), over the input
 /// service. See library/runtime/input.zig and system/services/input/.
 pub const input = @import("input.zig");

system/services/acpi/acpi.zig

@@ -16,7 +16,7 @@ const aml = @import("aml");
 const acpi_ids = @import("acpi-ids");
 const device = runtime.device;
 const protocol = @import("device-manager-protocol");
-const power = runtime.power_protocol;
+const power = @import("power-protocol");
 /// AML opcode/prefix bytes by name (`zero_opcode`, `byte_prefix`, …) — so the `_HID`
 /// integer decode names the opcodes instead of bare 0x0A/0x0B/… (docs/coding-standards.md).
 const opcodes = aml.opcodes;

system/services/init/init.zig

@@ -19,7 +19,7 @@
 
 const std = @import("std");
 const runtime = @import("runtime");
-const power = runtime.power_protocol;
+const power = @import("power-protocol");
 const build_options = @import("build_options");
 
 /// The system services init brings up at boot, in order, by binary path. This is