Switch to .NET 8 for cross-platform build support

- Target net8.0-windows instead of net4.8
- EnableWindowsTargeting for Linux build
- Replace Marshal.GetActiveObject with P/Invoke (not in .NET 8)
- Use NuGet package for Outlook Interop instead of local DLL ref
- Update Inno Setup script for .NET 8 runtime check
- Builds successfully on Linux, runs on Windows

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

src/StarfaceOutlookSync/StarfaceOutlookSync.csproj

@@ -2,9 +2,8 @@
 
   <PropertyGroup>
     <OutputType>WinExe</OutputType>
-    <TargetFramework>net4.8</TargetFramework>
+    <TargetFramework>net8.0-windows</TargetFramework>
     <UseWindowsForms>true</UseWindowsForms>
-    <ApplicationIcon>Resources\app.ico</ApplicationIcon>
     <AssemblyTitle>Starface Outlook Sync</AssemblyTitle>
     <Company>HackerSoft - Hacker-Net Telekommunikation</Company>
     <Product>Starface Outlook Sync</Product>
@@ -13,21 +12,14 @@
     <FileVersion>0.0.0.1</FileVersion>
     <Description>Synchronisiert Outlook-Kontakte mit Starface Telefonanlage</Description>
     <Copyright>Stefan Hacker - HackerSoft</Copyright>
+    <RuntimeIdentifier>win-x64</RuntimeIdentifier>
+    <SelfContained>false</SelfContained>
+    <EnableWindowsTargeting>true</EnableWindowsTargeting>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Reference Include="Microsoft.Office.Interop.Outlook">
-      <HintPath>$(ProgramFiles)\Microsoft Office\root\Office16\ADDINS\Microsoft.Office.Interop.Outlook.dll</HintPath>
-      <Private>false</Private>
-    </Reference>
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <EmbeddedResource Include="Resources\app.ico" />
+    <PackageReference Include="Microsoft.Office.Interop.Outlook" Version="15.0.4797.1004" />
   </ItemGroup>
 
 </Project>