docs: show the sign-in screens, from proxy admin to phone

Three screenshots the automation could not take: NPM's own login page,
the browser prompt in front of mc-webui, and the wrapper's Sign in
dialog on a real phone - the last one being the whole point of the
Android work, and the one thing no amount of prose conveys.

The two that carried a real hostname were retouched to mesh.example.com,
matching the rest of the guide and keeping a private address out of the
repository history. The phone shot is cropped to the dialog so it stays
legible at the width the page renders it. It lives in android-app.md
next to the feature it illustrates rather than in the HTTPS guide, which
already links there.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0187QpThw1Y8n7aYDjHtMHax

docs/android-app.md

@@ -130,7 +130,9 @@ If your instance sits behind a reverse proxy configured to require a login
 (HTTP Basic authentication — for example an **Access List** in Nginx Proxy
 Manager), the app asks for it the first time it connects, from version 1.3:
 
-> **Sign in** — *mc-webui.example.com asks for a username and password.*
+<p align="center">
+  <img src="../images/android-wrapper-signin.png" width="330" alt="mc-webui Android app - sign-in dialog for a server that requires a password">
+</p>
 
 Enter the username and password your proxy expects and tap **SIGN IN**. They are
 remembered per server address, so later launches go straight in. Get them wrong