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/JdeScoping.Client/Services/ISearchValidationService.cs

@@ -0,0 +1,19 @@
+using JdeScoping.Client.Components.Search;
+using JdeScoping.Client.Models;
+
+namespace JdeScoping.Client.Services;
+
+/// <summary>
+/// Service for validating search criteria before submission.
+/// </summary>
+public interface ISearchValidationService
+{
+    /// <summary>
+    /// Validates that a search is ready for submission.
+    /// </summary>
+    /// <param name="search">The search view model to validate.</param>
+    /// <param name="selectedSearchType">The selected search type ID.</param>
+    /// <param name="visibilityManager">The filter visibility manager with current filter state.</param>
+    /// <returns>A validation error message, or null if valid.</returns>
+    string? Validate(SearchViewModel search, int? selectedSearchType, FilterVisibilityManager visibilityManager);
+}