Tabs, one offline banner, background installs, drop anywhere

The page was one 6,800px scroll with nine nav links (hidden below 1150px).
It is now four tabs, Home, Games, Android and Tools, switched with 1-4; old
section links still land on the right tab.

When the Frame can't be reached, the server turns ssh's connection errors into
one plain message (503, offline: true), the page shows a single banner with
Retry and Set Up Connection, retries every 8 s, and reloads every panel when
the Frame answers. Panels say "Waiting for the Frame" instead of raw ssh text.

Flatpak and Android catalogue installs run as background jobs the page polls,
so a slow install no longer holds a request for up to 15 minutes or reports a
false failure; the bottom bar counts running installs.

Files can be dropped anywhere in the window, as the README already said.
Recent reports show the newest five, with Show all. Android display explains
an empty or failed read. A topped-up headset on a charger reads as not
charging rather than "still draining, using 0.0 W".

Fixes a race where the catalogue and reports loads wrote the compat-db
mirror's .tmp file at once and one failed with a 500.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/frame-control.md

@@ -17,6 +17,15 @@ python3 ui/server.py         # anywhere: then open http://127.0.0.1:47810
 
 ## Features
 
+The window has four tabs: **Home** (headset view, status, screenshots),
+**Games** (installed games, sideloaded titles, getting games), **Android** (apps,
+the catalogue, display settings, reports) and **Tools** (sending files and text,
+Flatpaks, remote and power). Keys 1–4 switch between them. Files can be dropped
+anywhere in the window. When the Frame can't be reached, one banner says why in
+plain words and the app retries every few seconds, filling everything in once it
+answers. Flatpak and Android installs run in the background; the bottom bar
+counts them while they run.
+
 - **Headset view**: what the lenses show, as SteamVR composites it (the room,
   floating panels, dashboard and controllers). Shows the left eye, like pointing
   a camera into one lens, or both eyes, as a single shot; saves as PNG. **Live**