Added PowerPoint templates to the Slide Assistant (#1055)

Co-authored-by: Thorsten Sommer <SommerEngineering@users.noreply.github.com>

app/MindWork AI Studio/Tools/DroppedFolder.cs

@@ -0,0 +1,36 @@
+namespace AIStudio.Tools;
+
+/// <summary>
+/// Picks the folder which a picker for exactly one folder takes from the paths dropped onto it.
+/// </summary>
+public static class DroppedFolder
+{
+    private static string TB(string fallbackEN) => PluginSystem.I18N.I.T(fallbackEN, typeof(DroppedFolder).Namespace, nameof(DroppedFolder));
+
+    /// <summary>
+    /// Finds the first dropped path which leads to a folder.
+    /// </summary>
+    /// <remarks>
+    /// A picker carries exactly one folder, so a multi-selection cannot be honored as a whole. A
+    /// dropped file is rejected instead of being taken as its parent folder. Everything a folder
+    /// contains is processed, so guessing the parent of a mistakenly dropped file could pull in far
+    /// more data than the user meant to hand over.
+    /// </remarks>
+    /// <param name="paths">The dropped paths, in the order the runtime delivered them.</param>
+    /// <returns>The path of the folder to take, or null when no dropped path leads to a folder.</returns>
+    public static string? FirstUsable(IReadOnlyList<string> paths) => paths.FirstOrDefault(Directory.Exists);
+
+    /// <summary>
+    /// Explains why none of the dropped paths could be used.
+    /// </summary>
+    /// <param name="paths">The dropped paths.</param>
+    public static string WarningFor(IReadOnlyList<string> paths)
+    {
+        // Naming the actual mistake beats a generic "that did not work". Dropping a file onto a
+        // folder picker is the likeliest of them:
+        if (paths.Any(File.Exists))
+            return TB("Please drop a folder, not a file.");
+
+        return TB("The dropped folder could not be accessed. Please choose it with the folder chooser instead.");
+    }
+}