refactor: address code review findings across all projects

Apply comprehensive fixes from code reviews including:
- Extract shared utilities (SqlFormatHelper, CellValueConverter, DbDestinationBase)
- Add interface abstractions (IAuthenticationService, IDatabaseMigrator, IMisQueryBuilder)
- Implement SecureStore for encrypted secrets storage
- Fix error handling with proper HTTP status codes and logging
- Optimize double enumeration in DevEtlRegistry
- Add DataSync.Dev README for developer onboarding
- Extract filter panel base classes to reduce duplication
- Update code review docs to mark all issues as fixed

NEW/src/Utils/JdeScoping.SecureStoreManager/Converters/BooleanConverters.cs

@@ -0,0 +1,85 @@
+using System.Globalization;
+using Avalonia.Data.Converters;
+
+namespace JdeScoping.SecureStoreManager.Converters;
+
+/// <summary>
+/// Inverts a boolean value.
+/// </summary>
+public class InverseBooleanConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is bool boolValue)
+        {
+            return !boolValue;
+        }
+        return false;
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is bool boolValue)
+        {
+            return !boolValue;
+        }
+        return false;
+    }
+}
+
+/// <summary>
+/// Converts a boolean to a visibility icon (eye open/closed).
+/// </summary>
+public class BooleanToVisibilityIconConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is bool isVisible)
+        {
+            // Use simple text icons for cross-platform compatibility
+            return isVisible ? "Hide" : "Show";
+        }
+        return "Show";
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}
+
+/// <summary>
+/// Converts null to bool (null = false, not null = true).
+/// </summary>
+public class NullToBoolConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        return value != null;
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}
+
+/// <summary>
+/// Converts a string to bool (empty = false, not empty = true).
+/// </summary>
+public class StringToBoolConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        if (value is string str)
+        {
+            return !string.IsNullOrWhiteSpace(str);
+        }
+        return false;
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotImplementedException();
+    }
+}