WOW !!! i got it worked !! finally !
just wanna share my founding …i m not gonna point all details ( i properly forgot anyway )
but what made it works if the method i use are not perfect PLEASE PLEASE PLEASE give me a better solution or another way around 
so basically /etc/config/syncthing “0” into “1”; “root” into “synching”
in /etc/in.it.d/syncthing “root” into “synching”
then
uci set fstab.@mount[-1].options=“umask=000”
uci commit fstab
block umount
block mount
this set the basic level my monts as everyone can read and write . which is the only way i can think of including syncthing .
if you have a way to change the permission of mounted device. to allow syncthing RW. without breaking the stock samba ( /proc/mounts auto change into ro ) pls do share with me. ;)))))