feat(app): version in window title and Help overlay

- csproj: add <Version>0.9.0</Version> as single source of truth
- AppVersion reads Major.Minor.Build from the assembly; WindowTitle
  exposes "Palladium Wallet 0.9.0" bound to Window.Title
- Menu Help → in-app overlay (same pattern as settings/server overlays)
  showing app name, version and a short description; backdrop tap and
  Esc close it
- i18n: menu.help, help.title, help.info in all 6 languages

src/App/PalladiumWallet.App.csproj

@@ -2,6 +2,9 @@
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
     <TargetFramework>net8.0</TargetFramework>
+    <!-- Versione dell'applicazione: unico punto da modificare. Compare nel
+         titolo della finestra ed è incisa nei binari pubblicati. -->
+    <Version>0.9.0</Version>
     <Nullable>enable</Nullable>
     <ApplicationManifest>app.manifest</ApplicationManifest>
     <ApplicationIcon>Assets\logo.ico</ApplicationIcon>