Optimize prepared asset package v2

src/AcDream.Launcher/ViewModels/FirstRunInstallerViewModel.cs

@@ -466,10 +466,9 @@ public sealed class FirstRunInstallerViewModel : ObservableObject, IDisposable
         string estimate = migration.Kind == ContentWorkKind.Overlay
             ? $"Affected filters: {migration.EffectiveDatIds.Count:N0} DAT id(s), "
                 + $"{migration.EffectiveLandblocks.Count:N0} landblock(s)."
-            : _contentUpdateBase is { PreparedAssetSize: > 0 } record
-                ? $"Free-space guidance: allow about "
-                    + $"{Math.Ceiling(record.PreparedAssetSize * 1.1 / (1024d * 1024d * 1024d)):N0} GiB."
-                : "Free-space guidance: allow room for one complete replacement pak.";
+            : $"Free-space guidance: allow at least "
+                + $"{LauncherInstaller.FullRebuildRequiredFreeBytes / (1024d * 1024d * 1024d):N0} GiB "
+                + "while the optimized package is built beside the active one.";
         return $"This client needs recipe {migration.TargetRecipeVersion}: "
             + $"{migration.Reason}. acdream will build {work} from your installed "
             + "Asheron's Call DAT files. The existing package stays in place "