Fix nullable warnings and improve exe file detection

Co-authored-by: JusterZhu <11714536+JusterZhu@users.noreply.github.com>

Author: Copilot

src/Common/CsprojReader.cs

@@ -144,8 +144,22 @@ private static string FindExeFile(string directory, string baseName)
 
         try
         {
+            // First try to find .exe file (Windows)
             var exeFiles = Directory.GetFiles(directory, $"{baseName}.exe", SearchOption.AllDirectories);
-            return exeFiles.FirstOrDefault() ?? string.Empty;
+            if (exeFiles.Any())
+                return exeFiles.First();
+
+            // Then try to find executable without extension (Linux/Mac)
+            var allFiles = Directory.GetFiles(directory, baseName, SearchOption.AllDirectories);
+            foreach (var file in allFiles)
+            {
+                var fileInfo = new FileInfo(file);
+                // Check if file is executable (on Unix systems) or if it's an exact match
+                if (fileInfo.Name == baseName)
+                    return file;
+            }
+
+            return string.Empty;
         }
         catch (Exception ex)
         {

src/Models/ConfigInfo.cs

@@ -8,26 +8,26 @@ namespace GeneralUpdate.Tool.Avalonia.Models;
 public class ConfigInfo
 {
     [JsonProperty("reportUrl")]
-    public string ReportUrl { get; set; }
+    public string ReportUrl { get; set; } = string.Empty;
 
     [JsonProperty("updateUrl")]
-    public string UpdateUrl { get; set; }
+    public string UpdateUrl { get; set; } = string.Empty;
 
     [JsonProperty("appName")]
-    public string AppName { get; set; }
+    public string AppName { get; set; } = string.Empty;
 
     [JsonProperty("mainAppName")]
-    public string MainAppName { get; set; }
+    public string MainAppName { get; set; } = string.Empty;
 
     [JsonProperty("clientVersion")]
-    public string ClientVersion { get; set; }
+    public string ClientVersion { get; set; } = string.Empty;
 
     [JsonProperty("packetName")]
-    public string PacketName { get; set; }
+    public string PacketName { get; set; } = string.Empty;
 
     [JsonProperty("format")]
-    public string Format { get; set; }
+    public string Format { get; set; } = string.Empty;
 
     [JsonProperty("encoding")]
-    public string Encoding { get; set; }
+    public string Encoding { get; set; } = string.Empty;
 }