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>

InstaSoftOfficeTool.csproj

@@ -1,27 +0,0 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <OutputType>WinExe</OutputType>
-    <TargetFramework>net48</TargetFramework>
-    <UseWPF>true</UseWPF>
-    <RootNamespace>InstaSoftOfficeTool</RootNamespace>
-    <AssemblyName>InstaSoftOfficeTool</AssemblyName>
-    <ApplicationIcon>Resources\app.ico</ApplicationIcon>
-    <Company>InstaSoft Zrt.</Company>
-    <Product>InstaSoft Office Tool</Product>
-    <Copyright>Copyright (c) InstaSoft Zrt. 2026</Copyright>
-    <Version>1.1.4</Version>
-    <AssemblyVersion>1.1.4.0</AssemblyVersion>
-    <FileVersion>1.1.4.0</FileVersion>
-    <ApplicationManifest>app.manifest</ApplicationManifest>
-    <LangVersion>latest</LangVersion>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.3" PrivateAssets="all" />
-    <Reference Include="System.Net.Http" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <Resource Include="Resources\app.ico" />
-  </ItemGroup>
-</Project>