v0.16.0 — ThemedMessageBox replacing native MessageBox everywhere

The Win32 MessageBox uses the system white-on-gray look that clashes
with the launcher's dark theme (jarring transition every time we
confirm a cancel, show an error, etc.). Replaced with a custom WPF
dialog that:

- Drops in : same Show(message, title, button, icon, default) API as
  System.Windows.MessageBox, returns the same MessageBoxResult.
- Looks native to the launcher : dark Brush.Bg.Window background,
  Brush.Border outline, Brush.Text.Primary content, AccentButton for
  the default action and SecondaryButton for the others.
- Iconography by emoji + colour code : ⛔ red (Error), ⚠ amber (Warning),
  ❓ neutral (Question), ℹ blue (Information). Mapped from MessageBoxImage.
- Buttons localised via Strings.ActionOk / ActionYes / ActionNo /
  ActionCancel — works in fr/en/zh/th/ar like the rest of the UI.
- Owner = currently active window (falls back to MainWindow then
  CenterScreen) so it positions correctly even from a child dialog.
- Esc resolves to Cancel/No matching MessageBox semantics.

The 21 MessageBox.Show call sites across MainViewModel, SettingsViewModel,
LicenseDetailsDialog and MainWindow now use ThemedMessageBox.Show with
no signature change — full grep replace + tiny `using` adjustments.

Versions bumped to 0.16.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.Core/Localization/Strings.cs

@@ -102,6 +102,9 @@ public static class Strings
     public static string ActionInstall      => T("⬇  Installer",    "⬇  Install",      "⬇  安装", "⬇  ติดตั้ง",  "⬇  تثبيت");
     public static string ActionInstallBig   => T("⬇  INSTALLER",    "⬇  INSTALL",      "⬇  安装", "⬇  ติดตั้ง",  "⬇  تثبيت");
     public static string ActionCancel       => T("Annuler",         "Cancel",          "取消",   "ยกเลิก",     "إلغاء");
+    public static string ActionOk           => T("OK",              "OK",              "确定",   "ตกลง",       "موافق");
+    public static string ActionYes          => T("Oui",             "Yes",             "是",     "ใช่",        "نعم");
+    public static string ActionNo           => T("Non",             "No",              "否",     "ไม่",        "لا");
     public static string ActionLater        => T("Plus tard",       "Later",           "稍后",   "ภายหลัง",    "لاحقاً");
     public static string ActionSave         => T("Enregistrer",     "Save",            "保存",   "บันทึก",     "حفظ");
     public static string ActionClose        => T("Fermer",          "Close",           "关闭",   "ปิด",        "إغلاق");