fix: support pid > 65535 (remove assert, use lower 16 bits)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: root

common/pid.c

@@ -39,8 +39,7 @@ npid_t PID;
 void init_common_PID (void) {
   if (!PID.pid) {
     int p = getpid ();
-    assert (!(p & 0xffff0000));
-    PID.pid = p;
+    PID.pid = (unsigned short) (p & 0xffff);
   }
   if (!PID.utime) {
     PID.utime = time (0);