dosutils: add GPL-2 headers and file descriptions

Add GPL-2-or-later license headers to the DOS utility source files and
document the purpose and local dependencies of each C, header and assembler
file.

Preserve the original Martin Stover copyright attribution for the historic
MARS-NWE utility sources, including files that did not previously carry an
explicit header but are part of the original tool set. Add Mario Fetka as the
2026 copyright holder for the current maintenance work, and use Mario-only
headers for files without original Martin Stover ownership.

Also add a root-level COPYING file containing the GPL-2 license text.

remove.c

@@ -1,4 +1,26 @@
-/* remove.c - Novell REMOVE-like DOS utility */
+/*
+ * mars-nwe-dosutils - NetWare/DOS utility tools.
+ *
+ * Copyright (C) 2026 Mario Fetka
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * Purpose: REMOVE utility for removing trustee rights from NetWare directories and files.
+ * Depends on: net.h, c32ncp.h, trustee.h/trustee.c trustee helpers, netcall.c requester helpers, tools.c shared utility routines.
+ */
 
 #include "net.h"
 #include "c32ncp.h"