feat(kernel,gui): NT I/O Manager (IRP-based drivers) + Registry Editor

Kernel (NT I/O subsystem):
- kernel/nt/io.c + include/kernel/nt/io.h (new): DRIVER_OBJECTs with a
  MajorFunction dispatch table, DEVICE_OBJECTs that can be stacked (attached),
  and IRPs pushed down the stack via io_call_driver / completed with
  io_complete_request. Ships three demo drivers: \Driver\Null (write sink,
  EOF reads), \Driver\Zero (zero-filled reads), and \Driver\Monitor -- a filter
  attached above \Device\Null that counts and forwards each IRP down the stack.
  Wired into the [12/14] boot step.
- LazyBox `iodev` lists drivers/devices with the stack and IRP counters, then
  runs a live demo: a WRITE IRP through the filtered Null stack and a READ from
  the Zero device.

GUI:
- gui/gui_apps.c: "Registry Editor" -- navigate the NT \Registry hive tree,
  click subkeys to descend and ".." to go up, with a values pane showing each
  value's name/type/data. Registered in the app table (start menu).

Verified live in the GUI terminal (screenshotted): 3 drivers / 3 devices, the
NullMonitor->Null device stack, a 16-byte WRITE sunk through the filter
(status 0x0), and an 8-byte zeroed READ from \Device\Zero. Clean build on
x86_64/aarch64/armv8i; 0 panics / 0 OOM.

Co-Authored-By: Claude Opus 4.8 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Fh5z6V7nGPbHvqVG5p4CXX

gui/gui_desktop.c

@@ -59,6 +59,7 @@ static const desktop_app_t g_apps[] = {
     { "Life",       GUI_ICON_FLASK,    gui_app_life_launch,     240,  70, 480, 380 },
     { "Rust Lab",   GUI_ICON_INFO,     gui_app_rustlab_launch,  300,  80, 420, 300 },
     { "Objects",    GUI_ICON_TASKS,    gui_app_objbrowse_launch,280,  70, 460, 340 },
+    { "RegEdit",    GUI_ICON_SETTINGS, gui_app_regedit_launch,  300,  90, 480, 360 },
     { "Clock",      GUI_ICON_CLOCK,    gui_app_clock_launch,    460, 120, 280, 260 },
     { "Settings",   GUI_ICON_SETTINGS, gui_app_settings_launch, 160,  60, 400, 320 },
     { "About",      GUI_ICON_INFO,     gui_app_about_launch,    240, 140, 330, 170 },
@@ -67,8 +68,8 @@ static const desktop_app_t g_apps[] = {
 
 // Which of the above appear on the desktop itself.
 // Indices into g_apps[]: Terminal, Files, Monitor, Kernel Log, KTest, Life,
-// Rust Lab, Settings. (Objects lives in the start menu.)
-static const int g_desktop_icons[] = { 0, 1, 2, 4, 5, 9, 10, 13 };
+// Rust Lab, Settings. (Objects/RegEdit live in the start menu.)
+static const int g_desktop_icons[] = { 0, 1, 2, 4, 5, 9, 10, 14 };
 #define DESKTOP_ICON_COUNT ((int)(sizeof(g_desktop_icons) / sizeof(g_desktop_icons[0])))
 
 static bool g_start_menu_open   = false;