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

docs/milestones/U1.md

@@ -1,6 +1,6 @@
 # U1 — Look and feel
 
-**Status:** in progress. The help key (issue #69) is merged; the website's key tables generated from the same lists (issue #72) are in a pull request. Screen recording (#17) and the rest of the milestone are not started.
+**Status:** in progress. Shipped: the help key (issue #69) and the key tables the website shares with it (#72), both in **v0.13.0**; the screenshot key (#83, **v0.17.0**). Not started: screen recording (#17), a Launcher of tiles (#9), themes (#10).
 
 **Goal:** the interface is consistent and uncrowded: the same thing is done the same way on every screen, and the 135 pixels of height go to content.