Refactor project structure in solution

Replaced "EnvelopeGenerator.WebUI" with "EnvelopeGenerator.Server" and "EnvelopeGenerator.WebUI.Client" with "EnvelopeGenerator.Server.Client". Updated project entries, solution configuration platforms, and nested projects to reflect these changes.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Layout/Header.razor

@@ -0,0 +1,21 @@
+<nav class="navbar header-navbar p-0">
+    <button class="navbar-toggler bg-primary d-block" @onclick="OnToggleClick">
+        <span class="navbar-toggler-icon"></span>
+    </button>
+    <div class="ms-3 fw-bold title pe-4">EnvelopeGenerator.ReceiverUI</div>
+</nav>
+
+@code {
+    [Parameter] public bool ToggleOn { get; set; }
+    [Parameter] public EventCallback<bool> ToggleOnChanged { get; set; }
+
+    async Task OnToggleClick() => await Toggle();
+
+    async Task Toggle(bool? value = null) {
+        var newValue = value ?? !ToggleOn;
+        if(ToggleOn != newValue) {
+            ToggleOn = newValue;
+            await ToggleOnChanged.InvokeAsync(ToggleOn);
+        }
+    }
+}