init: launch display-demo at boot

Spawn the display-demo client alongside the compositor so a normal boot shows
the moving scene (wallpaper + sliding rectangle + cursor) — the GUI track's
visible payoff. A demo fixture: drop it from boot_services to boot to a bare
compositor.

system/services/init/init.zig

@@ -30,7 +30,7 @@ const log_path = "/mnt/usb/DANOS.LOG";
 /// microkernel keeps such choices in user space, not the kernel. Drivers are absent
 /// on purpose: the device manager owns those. (A future init reads this from a
 /// manifest under /system/services instead of a hardcoded list.)
-const boot_services = [_][]const u8{ "vfs", "input", "device-manager", "fat", "display" };
+const boot_services = [_][]const u8{ "vfs", "input", "device-manager", "fat", "display", "display-demo" };
 
 var children: [boot_services.len]u32 = .{0} ** boot_services.len;
 var child_count: usize = 0;