Refactor cache validation and add startup cleanup

- Move cache folder completeness check to CacheHelper utility
- Replace Width with RightOffset in screenshot crop config
- Add startup cleanup to remove incomplete cache folders
- Validate cache folders before use in BomRadarService

Utilities/CacheHelper.cs

@@ -0,0 +1,51 @@
+namespace BomLocalService.Utilities;
+
+/// <summary>
+/// Utility methods for cache folder validation and operations.
+/// </summary>
+public static class CacheHelper
+{
+    /// <summary>
+    /// Checks if a cache folder is complete (has all required files).
+    /// A complete cache folder must have:
+    /// - All 7 frame images (frame_0.png through frame_6.png)
+    /// - metadata.json file
+    /// - frames.json file
+    /// </summary>
+    /// <param name="cacheFolderPath">The path to the cache folder to check</param>
+    /// <returns>True if the folder is complete, false otherwise</returns>
+    public static bool IsCacheFolderComplete(string cacheFolderPath)
+    {
+        if (string.IsNullOrEmpty(cacheFolderPath) || !Directory.Exists(cacheFolderPath))
+        {
+            return false;
+        }
+
+        // Check for all 7 frames
+        for (int i = 0; i < 7; i++)
+        {
+            var framePath = FilePathHelper.GetFrameFilePath(cacheFolderPath, i);
+            if (!File.Exists(framePath))
+            {
+                return false;
+            }
+        }
+
+        // Check for metadata.json
+        var metadataPath = FilePathHelper.GetMetadataFilePath(cacheFolderPath);
+        if (!File.Exists(metadataPath))
+        {
+            return false;
+        }
+
+        // Check for frames.json
+        var framesMetadataPath = FilePathHelper.GetFramesMetadataFilePath(cacheFolderPath);
+        if (!File.Exists(framesMetadataPath))
+        {
+            return false;
+        }
+
+        return true;
+    }
+}
+

Utilities/FilePathHelper.cs

@@ -88,5 +88,14 @@ public static class FilePathHelper
     {
         return Path.Combine(cacheFolderPath, ".writing");
     }
+
+    /// <summary>
+    /// Gets the frames metadata file path within a cache folder.
+    /// Format: "{CacheFolderPath}/frames.json"
+    /// </summary>
+    public static string GetFramesMetadataFilePath(string cacheFolderPath)
+    {
+        return Path.Combine(cacheFolderPath, "frames.json");
+    }
 }