Add EnvelopeGenerator.ReceiverUI project and UI components

Introduced a new Razor Components-based web application, `EnvelopeGenerator.ReceiverUI`, to the solution. This includes:

- Added `EnvelopeGenerator.ReceiverUI` project to `EnvelopeGenerator.sln` with Debug and Release configurations.
- Created `EnvelopeGenerator.ReceiverUI.csproj` targeting `.NET 8.0` with nullable and implicit usings enabled.
- Added Razor components (`App.razor`, `Routes.razor`, `MainLayout.razor`, `NavMenu.razor`, `Counter.razor`, `Error.razor`, `Home.razor`, `Weather.razor`) for layout, navigation, and pages.
- Included styles (`MainLayout.razor.css`, `NavMenu.razor.css`, `app.css`) and assets (`favicon.png`, `bootstrap.min.css`).
- Configured logging and allowed hosts in `appsettings.json` and `appsettings.Development.json`.
- Added `Program.cs` to configure and run the application.
- Added `launchSettings.json` for development and debugging profiles.

These changes enable a modern, interactive web interface with Bootstrap styling and development-friendly configurations.

EnvelopeGenerator.ReceiverUI/Components/Pages/Counter.razor

@@ -0,0 +1,19 @@
+@page "/counter"
+@rendermode InteractiveServer
+
+<PageTitle>Counter</PageTitle>
+
+<h1>Counter</h1>
+
+<p role="status">Current count: @currentCount</p>
+
+<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>
+
+@code {
+    private int currentCount = 0;
+
+    private void IncrementCount()
+    {
+        currentCount++;
+    }
+}