chore: deprecate standalone SecureStoreManager utility

Move SecureStoreManager project and tests to Deprecated folder and remove
from solution. SecureStore functionality is now integrated into ConfigManager.

Deprecated/JdeScoping.SecureStoreManager/Services/IClipboardService.cs

@@ -0,0 +1,14 @@
+namespace JdeScoping.SecureStoreManager.Services;
+
+/// <summary>
+/// Abstraction for platform-specific clipboard operations.
+/// Enables unit testing of view models that need clipboard access.
+/// </summary>
+public interface IClipboardService
+{
+    /// <summary>
+    /// Copies text to the system clipboard.
+    /// </summary>
+    /// <param name="text">The text to copy.</param>
+    Task SetTextAsync(string text);
+}