refactor: use collection expressions and is-null pattern in remaining sites

SysManager/SysManager.Tests/EventLogServiceTests.cs

@@ -34,7 +34,7 @@ public void BuildXPath_WithSeverity_IncludesLevel()
     {
         var opt = new EventLogQueryOptions
         {
-            Severities = new List<EventSeverity> { EventSeverity.Error }
+            Severities = [EventSeverity.Error]
         };
         var result = InvokeBuildXPath(opt);
         Assert.Contains("Level=2", result);

SysManager/SysManager/Helpers/EqualityConverter.cs

@@ -17,7 +17,7 @@ public sealed class EqualityConverter : IValueConverter
 {
     public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
     {
-        if (value == null || parameter == null)
+        if (value is null || parameter is null)
             return false;
         return string.Equals(value.ToString(), parameter.ToString(), StringComparison.Ordinal);
     }

SysManager/SysManager/Models/TargetPreset.cs

@@ -74,8 +74,8 @@ public static class TargetPresets
             ("FACEIT UK",    "82.145.38.1"),
         });
 
-    public static readonly IReadOnlyList<TargetPreset> All = new[]
-    {
+    public static readonly IReadOnlyList<TargetPreset> All =
+    [
         Global, CS2Europe, FaceitEurope, PubgEurope, Streaming
-    };
+    ];
 }

SysManager/SysManager/Services/AppAlertService.cs

@@ -116,11 +116,11 @@ public void Stop()
     public static IReadOnlyList<AppInstallEntry> GetRegistryApps()
     {
         List<AppInstallEntry> apps = [];
-        var paths = new[]
-        {
+        string[] paths =
+        [
             @"SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall",
             @"SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall"
-        };
+        ];
 
         foreach (var path in paths)
         {

SysManager/SysManager/Services/DeepCleanupService.cs

@@ -253,11 +253,11 @@ private static IReadOnlyList<CleanupCategory> Scan(IProgress<ScanProgress>? prog
 
     private static string[] SteamRoots(string pfx86, string pf)
     {
-        var roots = new List<string>
-        {
+        List<string> roots =
+        [
             Path.Combine(pfx86, "Steam"),
             Path.Combine(pf, "Steam"),
-        };
+        ];
         foreach (var drive in DriveInfo.GetDrives().Where(d => d.DriveType == DriveType.Fixed && d.IsReady))
         {
             var candidate = Path.Combine(drive.RootDirectory.FullName, "Steam");

SysManager/SysManager/Services/DuplicateFileService.cs

@@ -59,7 +59,7 @@ private static IReadOnlyList<DuplicateFileGroup> Scan(
             return [];
 
         // ── Pass 1: discover files and group by size ──
-        var sizeGroups = new Dictionary<long, List<FileInfo>>();
+        Dictionary<long, List<FileInfo>> sizeGroups = [];
         long discovered = 0;
         var stack = new Stack<string>();
         stack.Push(rootPath);

SysManager/SysManager/Services/FileShredderService.cs

@@ -195,7 +195,7 @@ public async Task ShredFolderAsync(string folderPath, ShredMethod method, IProgr
     private static List<string> EnumerateFilesSafe(string rootPath)
     {
         List<string> results = [];
-        var stack = new Stack<DirectoryInfo>();
+        Stack<DirectoryInfo> stack = [];
         stack.Push(new DirectoryInfo(rootPath));
 
         while (stack.Count > 0)