v1.16 — Remove PowerShell edition, restore flat project structure

PowerShell version removed — will use OV code signing certificate instead.
Files moved back from src/ to project root.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Models/InstalledOffice.cs

@@ -0,0 +1,11 @@
+namespace InstaSoftOfficeTool.Models
+{
+    public class InstalledOffice
+    {
+        public string DisplayName { get; set; }
+        public string Version { get; set; }
+        public string ProductCode { get; set; }
+        public bool IsClickToRun { get; set; }
+        public bool IsSelected { get; set; }
+    }
+}