Add get_interface_ip() helper to resolve an interface's IPv4 address
via 'ip -o addr show'. Use it to back-propagate gateway into DHCP
ranges so clients receive their default route.
- set_dhcp_range() resolves gateway: explicit > existing range > iface IP
- DnsToFirewallSync and FirewallToDhcpSync sync ensure gateways are set
- Remove automatic masquerade toggle from DnsToFirewallSync
- Fix dnsmasq lease file path to /var/lib/misc/dnsmasq.leases
- Rename lease state field expires_at -> expires (ISO string)
- Add 'ip -o addr show' to sudo whitelist
Add EventBus with loop guards to keep firewall, dnsmasq, wireguard,
and network configs consistent. Handlers emit SyncEvent after mutations;
subscribers compute diffs and write JSON without manual cascade loops.
mteehan