Fix: Incomplete RFC 1918 check for 172.x.x.x in launcher

## TL;DR
The launcher's LAN IP detection matches all 172.x.x.x addresses, but only 172.16-31.x.x is private.

## Current State
`ip.StartsWith("172.")` matches public IPs like 172.200.x.x, potentially showing a non-LAN URL.

## Desired State
Only match the actual private range: 172.16.0.0 through 172.31.255.255.