As others have pointed out, your dnsmasq file still has some leftovers from AGH install. I made an uninstall script from my manual install thread that removes all AGH options and resets your dnsmasq file back to a working config.
The reason you lost DNS is because AGH inserts itself as the primary DNS and pushes dnsmasq to port 5353 to be a resolver internal dns. Its sole use is for PTR lookups for your clients. A cleaner way to deploy AGH would be to disable OpenWrt's DHCP and switch over completely to AGH's DHCP but they still have some code refactoring to sort out for AGH. I and James decided that due to the state of AGH's DHCP that it would be wiser to do this split setup until AGH's DHCP improves to the level of OpenWrt's DHCP. Right now simple DHCP on a flat network will work but more complex networks with VLANs etc would be tricky to implement.
#include uninstall script.
uninstallAGH.sh
#!/bin/sh
curl -s -S -L https://raw.githubusercontent.com/AdguardTeam/AdGuardHome/master/scripts/install.sh | sh -s -- -v -u
# 1. Reverts AdGuard Home configuration and resets settings to default.
# 2. Enable rebind protection.
# 3. Remove DHCP options for IPv4 and IPv6
uci -q delete dhcp.@dnsmasq[0].noresolv
uci -q delete dhcp.@dnsmasq[0].cachesize
uci set dhcp.@dnsmasq[0].rebind_protection='1'
uci -q delete dhcp.@dnsmasq[0].server
uci -q delete dhcp.@dnsmasq[0].port
uci -q delete dhcp.lan.dhcp_option
uci -q delete dhcp.lan.dns
# Network Configuration
# Disable peer/ISP DNS
uci set network.wan.peerdns="0"
uci set network.wan6.peerdns="0"
# Configure DNS provider to Google DNS
uci -q delete network.wan.dns
uci add_list network.wan.dns="8.8.8.8"
uci add_list network.wan.dns="8.8.4.4"
# Configure IPv6 DNS provider to Google DNS
uci -q delete network.wan6.dns
uci add_list network.wan6.dns="2001:4860:4860::8888"
uci add_list network.wan6.dns="2001:4860:4860::8844"
# Save and apply
uci commit dhcp
uci commit network
/etc/init.d/network restart
/etc/init.d/dnsmasq restart
/etc/init.d/odhcpd restart