Docs: caught up with v0.13.0 to v0.19.0

The documentation had kept up feature page by feature page and nowhere
else. Now also:

- the home page's App cards (notes of any size, pictures, sharing) and its
  note (the Shell, the VPN, the screenshot key);
- the guide: VPN in the Status Bar and in Settings, the three keys that work
  everywhere, screenshots of the Shell, a picture, sharing, the VPN page and
  the help panel;
- three how-tos: move files with your phone, set up the VPN, take a
  screenshot; where the files are and what things cost in memory;
- the FAQ: screenshots, and what listens on the network;
- the README's opening: what the firmware does today;
- the glossary: Tunnel, Sharing, Screenshot;
- every milestone's status line, with the version each thing shipped in.

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

site/content/guide/vpn.md

@@ -4,6 +4,7 @@ description = "A WireGuard tunnel: reach your own network from any Wi-Fi, or sen
 weight = 12
 [extra]
 tag = "WireGuard"
+screens = ["vpn.png"]
 +++
 
 The Cardputer can join a **WireGuard** network over whatever Wi-Fi it is on. Two uses: reaching your own machines from anywhere (an IRC bouncer, the device's own [Debug Console](/dev/debug/)), and keeping its traffic private on a hotel or café network.