Change TunSettings to support separate IPv4/IPv6 MTU values and add gateway, DNS, autoSystemRoutingTable and autoOutboundsInterface properties. Introduces _normalizeMtu to accept legacy single-value or array forms and provide sensible defaults. Update fromJson/toJson to handle new fields and preserve backward compatibility. Update tun form UI to expose MTU IPv4/IPv6 inputs, Gateway/DNS tag selects, Auto Routing Table and Auto Outbounds input.
Introduces TUN protocol to inbound.js, including a new TunSettings class. Updates inbound form to support TUN protocol and adds a dedicated form template for TUN settings. Translation files are updated with TUN-related strings for all supported languages.
