Update auth, JSON config, and sender dashboard styles

Modified the `[Authorize]` attribute in `EnvelopeController` to use `AuthScheme.Sender` for authentication. Updated `Program.cs` to configure JSON serialization with `ReferenceHandler.IgnoreCycles` to handle circular references.

Added new CSS styles for the sender dashboard in `sender-page.css`, including layout, action bars, buttons, tabs, badges, and responsive design improvements. Enhanced button states and introduced styles for status indicators and receiver badges.

EnvelopeGenerator.Server/EnvelopeGenerator.Server/Controllers/EnvelopeController.cs

@@ -94,7 +94,7 @@ public class EnvelopeController : ControllerBase
     /// <param name="command"></param>
     /// <returns></returns>
     [NonAction]
-    [Authorize]
+    [Authorize(AuthenticationSchemes = AuthScheme.Sender)]
     [HttpPost]
     public async Task<IActionResult> CreateAsync([FromBody] CreateEnvelopeCommand command)
     {