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>

installer/setup.iss

@@ -36,7 +36,7 @@ Name: "autostart"; Description: "Bei Windows-Anmeldung automatisch starten"; Gro
 
 [Files]
 ; Hauptanwendung - Pfad anpassen nach Build
-Source: "..\src\StarfaceOutlookSync\bin\Release\net4.8\*"; DestDir: "{app}"; Flags: ignoreversion recursesubdirs createallsubdirs
+Source: "..\src\StarfaceOutlookSync\bin\Release\net8.0-windows\win-x64\*"; DestDir: "{app}"; Flags: ignoreversion recursesubdirs createallsubdirs
 
 [Icons]
 Name: "{group}\{#MyAppName}"; Filename: "{app}\{#MyAppExeName}"
@@ -57,26 +57,35 @@ Filename: "taskkill"; Parameters: "/F /IM {#MyAppExeName}"; Flags: runhidden; Ru
 Type: filesandordirs; Name: "{userappdata}\StarfaceOutlookSync"
 
 [Code]
-// Pruefe ob .NET Framework 4.8 installiert ist
-function IsDotNetInstalled(): Boolean;
+// Pruefe ob .NET 8 Desktop Runtime installiert ist
+function IsDotNet8Installed(): Boolean;
 var
-  Version: Cardinal;
+  ResultCode: Integer;
 begin
-  Result := RegQueryDWordValue(HKLM, 'SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full', 'Release', Version);
+  // dotnet --list-runtimes enthaelt "Microsoft.WindowsDesktop.App 8.x"
+  Result := Exec('dotnet', '--list-runtimes', '', SW_HIDE, ewWaitUntilTerminated, ResultCode);
   if Result then
-    Result := Version >= 528040; // .NET 4.8
+    Result := ResultCode = 0;
+  // Einfacher Check: dotnet.exe muss existieren
+  Result := FileExists(ExpandConstant('{commonpf}\dotnet\dotnet.exe')) or
+            FileExists(ExpandConstant('{commonpf64}\dotnet\dotnet.exe'));
 end;
 
 function InitializeSetup(): Boolean;
 begin
   Result := True;
 
-  if not IsDotNetInstalled() then
+  if not IsDotNet8Installed() then
   begin
-    MsgBox('.NET Framework 4.8 oder hoeher wird benoetigt.' + #13#10 +
-           'Bitte installieren Sie es von:' + #13#10 +
-           'https://dotnet.microsoft.com/download/dotnet-framework/net48',
-           mbError, MB_OK);
+    if MsgBox('.NET 8 Desktop Runtime wird benoetigt.' + #13#10 + #13#10 +
+              'Soll die Download-Seite geoeffnet werden?',
+              mbConfirmation, MB_YESNO) = IDYES then
+    begin
+      ShellExec('open', 'https://dotnet.microsoft.com/download/dotnet/8.0/runtime', '', '', SW_SHOWNORMAL, ewNoWait, ResultCode);
+    end;
     Result := False;
   end;
 end;
+
+var
+  ResultCode: Integer;