* fix(amneziawg): respect tunnel MTU when writing UDP replies
Send replies through gVisor FindRoute/Route.WritePacket instead of WriteRawPacket so the network endpoints apply the tunnel MTU and fragment oversized IPv4/IPv6 datagrams. Preserve UDP checksums including the zero-complement IPv6 case and validate lengths before narrowing to uint16.
Regression tests inspect and reassemble actual channel-backed TUN output at and above the MTU, verify checksums and exercise concurrent sources.
* docs(review): put the tally before Design and name who can store a trigger
