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>

Models/OfficeVersion.cs

@@ -1,9 +0,0 @@
-namespace InstaSoftOfficeTool.Models
-{
-    public enum OfficeVersion
-    {
-        Office2024,
-        Office2021,
-        Office2019
-    }
-}