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/Services/OutlookContactsService.cs

@@ -11,6 +11,17 @@ namespace StarfaceOutlookSync.Services
         private Outlook.Application _outlookApp;
         private bool _weStartedOutlook;
 
+        // Marshal.GetActiveObject existiert nicht in .NET 8, daher P/Invoke
+        [DllImport("oleaut32.dll", PreserveSig = false)]
+        private static extern void GetActiveObject([MarshalAs(UnmanagedType.LPStruct)] Guid rclsid, IntPtr pvReserved, [MarshalAs(UnmanagedType.IUnknown)] out object ppunk);
+
+        private static object GetActiveComObject(string progId)
+        {
+            var clsid = Type.GetTypeFromProgID(progId, true).GUID;
+            GetActiveObject(clsid, IntPtr.Zero, out var obj);
+            return obj;
+        }
+
         private Outlook.Application GetOutlookApp()
         {
             if (_outlookApp != null) return _outlookApp;
@@ -18,7 +29,7 @@ namespace StarfaceOutlookSync.Services
             try
             {
                 // Versuche laufende Outlook-Instanz zu finden
-                _outlookApp = (Outlook.Application)Marshal.GetActiveObject("Outlook.Application");
+                _outlookApp = (Outlook.Application)GetActiveComObject("Outlook.Application");
                 _weStartedOutlook = false;
             }
             catch

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>

src/StarfaceOutlookSync/UI/MainForm.cs

@@ -228,17 +228,17 @@ namespace StarfaceOutlookSync.UI
             }
         }
 
-        private async Task SyncSelectedProfile()
+        private Task SyncSelectedProfile()
         {
             if (_profileList.SelectedItems.Count == 0)
             {
                 MessageBox.Show("Bitte ein Profil auswaehlen.", "Sync",
                     MessageBoxButtons.OK, MessageBoxIcon.Information);
-                return;
+                return Task.CompletedTask;
             }
 
             var profile = _profileList.SelectedItems[0].Tag as SyncProfile;
-            if (profile == null) return;
+            if (profile == null) return Task.CompletedTask;
 
             using (var syncForm = new SyncProgressForm(profile))
             {
@@ -246,6 +246,7 @@ namespace StarfaceOutlookSync.UI
             }
 
             RefreshProfileList();
+            return Task.CompletedTask;
         }
 
         private async Task RunSync(SyncProfile profile)