Remove Tauri desktop shell

Not going to be used — drop src-tauri/ and all references to it in
the docs. MapTool stays a plain Sinatra web app for now.

README.adoc

@@ -3,8 +3,7 @@
 :toclevels: 2
 :source-highlighter: rouge
 
-A mapping application backend written in Ruby with Sinatra, optionally
-wrapped as a native desktop app with Tauri.
+A mapping application written in Ruby with Sinatra.
 
 The project's shape is still open — this is the initial scaffold.
 
@@ -12,14 +11,11 @@ The project's shape is still open — this is the initial scaffold.
 
 Early scaffold. The web application serves a vector map (MapLibre GL
 JS), with an online style and an optional offline style backed by a
-local PMTiles file; the desktop shell boots the same server inside a
-native window.
+local PMTiles file, plus an animated RainViewer radar overlay.
 
 == Requirements
 
 * Ruby (see `.ruby-version`) and Bundler
-* Rust and the Tauri CLI, only if you want to build the desktop shell
-  (see `docs/development.adoc`)
 
 == Getting started