feat: D-Bus + sessiond services wired into init.d

Added boot target hierarchy (boot_essential → boot_late) and
D-Bus services directly to base recipe init.d:
- 12_dbus.service: dbus-daemon --system
- 13_sessiond.service: redbear-sessiond (org.freedesktop.login1)
- 13_seatd.service: seatd seat management

D-Bus daemon confirmed running in QEMU boot. User lookup
warning (unknown username root) is a pre-existing Redox
D-Bus configuration issue.

recipes/core/base/P4-initfs-dbus-services.patch

@@ -0,0 +1 @@
+../../../local/patches/base/P4-initfs-dbus-services.patch

recipes/core/base/recipe.toml

@@ -16,6 +16,7 @@ patches = [
     "P4-initfs-usb-drm-services.patch",
     "P4-initfs-network-services.patch",
     "P4-initfs-getty-services.patch",
+    "P4-initfs-dbus-services.patch",
 ]
 
 [build]