One interesting thing is that I don't see the vpn network interface in your screenshot of interfaces -- so maybe it is not properly defined...
your network file should have the interface defined as follows:
config interface 'vpn'
option proto 'none'
option ifname 'tun0'
firewall (remove all vpn related rules and add the following):
config zone
option name 'vpn'
option input 'ACCEPT'
option forward 'REJECT'
option output 'ACCEPT'
option network 'vpn'
config forwarding
option dest 'wan'
option src 'vpn'
and your openvpn config file should have
option dev 'tun0'
also try adding to openvpn:
list push 'dhcp-option DNS 192.168.13.1'