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/_index.md

@@ -10,6 +10,8 @@ This guide says what the firmware does **today** and nothing else. Start with th
 
 **The mesh messenger is planned, not built.** The LoRa Scanner listens to Meshtastic traffic and shows it, but the device sends nothing yet: that is the next milestone and waits for a second node to test with.
 
+**Three things work on every screen:** <kbd>Fn</kbd> + <kbd>h</kbd> for the keys, <kbd>Fn</kbd> + <kbd>p</kbd> for a screenshot, and <kbd>Fn</kbd> + <kbd>`</kbd> to go back to the Launcher.
+
 Looking for a recipe or a quick answer? There are [how-tos](/howto/) and a [FAQ](/faq/).
 
 Something missing or wrong? Write to the [issue tracker](https://git.twis.la/twisla/roro9stack/issues) or to contact@roro9stack.net.