tools: add shared NCP22 name helper

Move the common NCP22 DOS name buffer helper into tools.c and declare it in
net.h.

Replace the local copy/uppercase implementations in CREATOR, FLAG, FLAGDIR,
NDIR and NWTESTS with tool_copy_ncp22_name(). The helper keeps the existing
behavior: uppercase conversion, path separator rejection and the 1..12 byte
DOS name length limit.

NCOPY is intentionally left untouched while its NCP copy path remains under
investigation.

tools.c

@@ -127,6 +127,37 @@ uint32 tool_get_dword_hl(uint8 *p)
          (uint32)p[3]);
 }
 
+/*
+ * tool_copy_ncp22_name
+ *
+ * Purpose:
+ *   Converts one DOS filename component into the uppercase NCP22 name format.
+ *   The helper rejects paths and keeps the historical 12-byte DOS namespace
+ *   component limit used by the old directory-entry NCPs.
+ */
+int tool_copy_ncp22_name(uint8 *dst, char *src, uint8 *len_out)
+{
+  char tmp[260];
+  int len;
+
+  if (!dst || !len_out)
+    return(-1);
+  if (!src)
+    src = "";
+
+  tool_upcopy(tmp, src, sizeof(tmp));
+  if (strchr(tmp, '\\') || strchr(tmp, '/') || strchr(tmp, ':'))
+    return(-1);
+
+  len = strlen(tmp);
+  if (len < 1 || len > 12)
+    return(-1);
+
+  memcpy(dst, tmp, len);
+  *len_out = (uint8)len;
+  return(0);
+}
+
 #ifdef __WATCOMC__
 /*
  * Borland C compatibility wrappers used by the historical mars-nwe DOS tools.