Add image preview support: Krea-tag parsing with modal, file-explorer preview, skill output endpoint, increase execute timeout to 180s

- SkillEndpoint: GET /api/skills/{slug}/output/{filename} for skill output files
- WorkspaceEndpoint: GET /api/workspace/raw for raw file serving (images)
- File-Explorer: Image preview for png/jpg/gif/webp/svg/bmp/ico
- Chat UI: Parse [Krea: filename] tags into clickable chips with image modal
- ToolService: Increase execute timeout from 30s to 180s for long-running skills

Services/ToolService.cs

@@ -256,7 +256,7 @@ public class ToolService
                 if (proc == null) return "Fehler: Prozess konnte nicht gestartet werden";
                 await proc.StandardInput.WriteAsync(command);
                 proc.StandardInput.Close();
-                var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));
+                var cts = new CancellationTokenSource(TimeSpan.FromSeconds(180));
                 try
                 {
                     await proc.WaitForExitAsync(cts.Token);
@@ -264,7 +264,7 @@ public class ToolService
                 catch (OperationCanceledException)
                 {
                     proc.Kill(entireProcessTree: true);
-                    return "Fehler: Timeout nach 30 Sekunden - Prozess abgebrochen";
+                    return "Fehler: Timeout nach 180 Sekunden - Prozess abgebrochen";
                 }
                 var stdout = await proc.StandardOutput.ReadToEndAsync();
                 var stderr = await proc.StandardError.ReadToEndAsync();