fix: CLI-Prozess bei Abbruch zuverlässig beenden (Kill on Cancel)

Process.Dispose() gibt nur den Handle frei, killt aber nicht den Prozess.
Jetzt wird per CancellationToken.Register() der gesamte Prozessbaum
(entireProcessTree: true) sofort beendet wenn der User auf Stoppen klickt.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Services/ClaudeCliService.cs

@@ -237,6 +237,13 @@ public class ClaudeCliService
             process.Start();
             process.BeginErrorReadLine();
 
+            // Bei Cancellation den gesamten Prozessbaum beenden
+            // (ReadLineAsync wirft OperationCanceledException, aber process.Dispose() killt NICHT den Prozess)
+            using var killOnCancel = cancellationToken.Register(() =>
+            {
+                try { if (!process.HasExited) process.Kill(entireProcessTree: true); } catch { }
+            });
+
             await process.StandardInput.WriteAsync(stdinPrompt);
             await process.StandardInput.FlushAsync();
             process.StandardInput.Close();
@@ -245,11 +252,6 @@ public class ClaudeCliService
             string line;
             while ((line = await reader.ReadLineAsync(cancellationToken)) != null)
             {
-                if (cancellationToken.IsCancellationRequested)
-                {
-                    try { process.Kill(entireProcessTree: true); } catch { }
-                    throw new OperationCanceledException();
-                }
 
                 if (!line.StartsWith("{"))
                     continue;
@@ -587,6 +589,11 @@ public class ClaudeCliService
             process.BeginOutputReadLine();
             process.BeginErrorReadLine();
 
+            using var killOnCancel = cancellationToken.Register(() =>
+            {
+                try { if (!process.HasExited) process.Kill(entireProcessTree: true); } catch { }
+            });
+
             await process.WaitForExitAsync(cancellationToken);
 
             result.ExitCode = process.ExitCode;