v1.15 — PowerShell edition + repo restructure

- New powershell/InstaSoftOfficeTool.ps1: single-file WPF GUI version
  - Same Fluent Design UI, no compilation needed
  - Runs on any Windows 7+ with PowerShell 5.1 (built-in)
  - Chrome won't flag .ps1 files as "rarely downloaded"
  - Auto-elevates to admin
- Moved C# source to src/ subfolder
- Updated .gitignore for nested bin/obj folders

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

Pages/VersionPage.xaml.cs

@@ -1,34 +0,0 @@
-using System.Windows.Controls;
-using InstaSoftOfficeTool.Models;
-
-namespace InstaSoftOfficeTool.Pages
-{
-    public partial class VersionPage : Page, IWizardPage
-    {
-        private readonly MainWindow _main;
-        private readonly InstallConfig _config;
-
-        public VersionPage(MainWindow main, InstallConfig config)
-        {
-            InitializeComponent();
-            _main = main;
-            _config = config;
-
-            // Restore selection
-            switch (_config.Version)
-            {
-                case OfficeVersion.Office2024: Rb2024.IsChecked = true; break;
-                case OfficeVersion.Office2021: Rb2021.IsChecked = true; break;
-                case OfficeVersion.Office2019: Rb2019.IsChecked = true; break;
-            }
-        }
-
-        public bool Validate()
-        {
-            if (Rb2024.IsChecked == true) _config.Version = OfficeVersion.Office2024;
-            else if (Rb2021.IsChecked == true) _config.Version = OfficeVersion.Office2021;
-            else if (Rb2019.IsChecked == true) _config.Version = OfficeVersion.Office2019;
-            return true;
-        }
-    }
-}