Initial scaffold: Sinatra map app with Tauri desktop shell

Sinatra backend serving a basic Leaflet map, wrapped in a Tauri
desktop shell that starts the same server in a native window.

app.rb

@@ -0,0 +1,17 @@
+require "sinatra/base"
+require "sinatra/json"
+
+module Maptool
+  class App < Sinatra::Base
+    set :public_folder, File.join(__dir__, "public")
+    set :views, File.join(__dir__, "views")
+
+    get "/" do
+      erb :index
+    end
+
+    get "/api/health" do
+      json status: "ok"
+    end
+  end
+end