Shell: ping, nslookup, port, traceroute, ifconfig and arp (#90)

Network troubleshooting from the device itself, in the Shell and over both
consoles. ping, nslookup, port and traceroute each run on a task of their
own and print as they go, to the console that asked; one at a time, and
`cancel` stops it. ifconfig and arp answer at once: the interfaces (Wi-Fi
and the VPN), which is the default route, the DNS servers, the neighbours.

nslookup asks a DNS server itself, so it can say which server answered and
in how long, and ask another. A sized ping finds what a tunnel really
carries.

With a how-to, "When the network doesn't work", and the rest of the docs.
tls, ntp and netstat from the issue's list are not in this.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

site/content/faq.md

@@ -73,6 +73,10 @@ In the Storage App, press <kbd>w</kbd>: the device serves a small web page to an
 
 <kbd>Fn</kbd> + <kbd>p</kbd>, on any screen. The picture goes to `/screenshots` on the SD card. See [Take a screenshot](/howto/screenshot/).
 
+## The network doesn't work: how do I find out why?
+
+From the device itself, in the Shell: `ifconfig`, `ping`, `nslookup`, `port` and `traceroute`. [When the network doesn't work](/howto/network-check/) puts them in order.
+
 ## Do I need an SD card?
 
 For the radio, GNSS position, Wi-Fi tools, IRC chat and Gemini browsing, no. For anything that is *kept*, yes: notes, IRC logs, Wi-Fi scan logs, GNSS Tracks, LoRa captures, saved Gemini pages and update files. See [Find your files on the SD card](/howto/sd-files/).