feat(android): QR code scanner for Send address field

Camera2 + ZXing.Net 0.16.9 activity (ScannerActivity) that captures JPEG
frames at ~2.5 fps and decodes QR codes without Xamarin dependencies.
Result is returned to MainActivity via OnActivityResult/TaskCompletionSource.
PlatformServices.ScanQrAsync seam wires Android head to shared App layer;
ScanQrCommand in the Send ViewModel strips BIP21 URI scheme/query parameters.
CAMERA permission and uses-feature added to AndroidManifest.

src/App/Localization/Loc.cs

@@ -183,6 +183,7 @@ public sealed class Loc
         ["send.all"]              = ["Invia tutto",                                                       "Send all",                     "Enviar todo",                          "Tout envoyer",                             "Enviar tudo",                              "Alles senden"],
         ["send.feerate"]          = ["fee sat/vB:",                                                       "fee sat/vB:",                  "tarifa sat/vB:",                       "frais sat/vB :",                           "taxa sat/vB:",                             "Gebühr sat/vB:"],
         ["send.prepare"]          = ["Prepara transazione",                                               "Prepare transaction",          "Preparar transacción",                 "Préparer la transaction",                  "Preparar transação",                       "Transaktion vorbereiten"],
+        ["send.scan"]             = ["Scansiona QR",                                                      "Scan QR",                      "Escanear QR",                          "Scanner QR",                               "Escanear QR",                              "QR scannen"],
         ["send.confirm"]          = ["CONFERMA E TRASMETTI",                                              "CONFIRM AND BROADCAST",        "CONFIRMAR Y TRANSMITIR",               "CONFIRMER ET DIFFUSER",                    "CONFIRMAR E TRANSMITIR",                   "BESTÄTIGEN UND SENDEN"],
 
         // Stato connessione

src/App/Services/PlatformServices.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Threading.Tasks;
+
+namespace PalladiumWallet.App.Services;
+
+/// <summary>
+/// Seam per servizi specifici della piattaforma (Android/desktop).
+/// Il head Android imposta i delegate in OnCreate; desktop li lascia null.
+/// </summary>
+public static class PlatformServices
+{
+    /// <summary>
+    /// Apre lo scanner QR nativo e restituisce il testo raw del codice,
+    /// oppure null se l'utente annulla o lo scanner non è disponibile.
+    /// </summary>
+    public static Func<Task<string?>>? ScanQrAsync { get; set; }
+}

src/App/ViewModels/MainWindowViewModel.Send.cs

@@ -3,6 +3,7 @@ using System.Threading.Tasks;
 using CommunityToolkit.Mvvm.ComponentModel;
 using CommunityToolkit.Mvvm.Input;
 using NBitcoin;
+using PalladiumWallet.App.Services;
 using PalladiumWallet.Core.Chain;
 using PalladiumWallet.Core.Net;
 using PalladiumWallet.Core.Wallet;
@@ -29,6 +30,18 @@ public partial class MainWindowViewModel
     [ObservableProperty]
     private bool hasPendingSend;
 
+    [RelayCommand]
+    private async Task ScanQr()
+    {
+        if (PlatformServices.ScanQrAsync is not { } scan) return;
+        var raw = await scan();
+        if (string.IsNullOrWhiteSpace(raw)) return;
+        // Gestisce URI tipo "palladium:ADDRESS?amount=X" estraendo solo l'indirizzo
+        var address = raw.Contains(':') ? raw.Split(':')[1] : raw;
+        if (address.Contains('?')) address = address.Split('?')[0];
+        SendTo = address.Trim();
+    }
+
     [RelayCommand]
     private async Task PrepareSend()
     {