Enhance IndexPage UI and navigation functionality

- Injected `NavigationManager` into `IndexPage.razor` to enable navigation.
- Improved layout alignment with additional classes in `<div>`.
- Added a new button for navigation to `/sender` with icons and text.
- Introduced a feature badge for "PDF-Export" with an SVG icon.
- Updated `.home-btn-primary` styles in `app.css`:
  - Ensured text color is always white with `!important`.
  - Made text bolder by increasing `font-weight` to `700`.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Pages/IndexPage.razor

@@ -1,5 +1,6 @@
 @page "/"
 @inject IJSRuntime JS
+@inject NavigationManager Navigation
 @rendermode InteractiveWebAssembly
 
 <link href="_content/DevExpress.Blazor.Themes/blazing-berry.bs5.min.css" rel="stylesheet" />
@@ -26,7 +27,18 @@
                     <span id="home-description"></span>
                 </p>
 
-                <div class="mt-4 pt-3 border-top">
+                <div class="mt-4 pt-3 border-top d-flex flex-column align-items-center gap-4">
+
+                    <button class="home-btn-primary btn px-4 py-2 d-flex align-items-center gap-2" @onclick='() => Navigation.NavigateTo("/sender")'>
+                        <svg xmlns="http://www.w3.org/2000/svg" width="18" height="18" fill="currentColor" viewBox="0 0 16 16">
+                            <path d="M0 4a2 2 0 0 1 2-2h12a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H2a2 2 0 0 1-2-2V4Zm2-1a1 1 0 0 0-1 1v.217l7 4.2 7-4.2V4a1 1 0 0 0-1-1H2Zm13 2.383-4.708 2.825L15 11.105V5.383Zm-.034 6.876-5.64-3.471L8 9.583l-1.326-.795-5.64 3.47A1 1 0 0 0 2 13h12a1 1 0 0 0 .966-.741ZM1 11.105l4.708-2.897L1 5.383v5.722Z"/>
+                        </svg>
+                        Zur Umschlag-Übersicht
+                        <svg xmlns="http://www.w3.org/2000/svg" width="16" height="16" fill="currentColor" viewBox="0 0 16 16">
+                            <path fill-rule="evenodd" d="M4.646 1.646a.5.5 0 0 1 .708 0l6 6a.5.5 0 0 1 0 .708l-6 6a.5.5 0 0 1-.708-.708L10.293 8 4.646 2.354a.5.5 0 0 1 0-.708z"/>
+                        </svg>
+                    </button>
+
                     <div class="d-flex flex-wrap justify-content-center gap-3">
                         <div class="home-feature-badge">
                             <svg xmlns="http://www.w3.org/2000/svg" width="15" height="15" fill="currentColor" class="me-1" viewBox="0 0 16 16">
@@ -48,6 +60,7 @@
                             PDF-Export
                         </div>
                     </div>
+
                 </div>
 
             </div>

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/css/app.css

@@ -308,8 +308,8 @@ article {
 .home-btn-primary {
     background: linear-gradient(135deg, #2c3e50 0%, #3498db 100%);
     border: none;
-    color: #fff;
-    font-weight: 500;
+    color: #fff !important;
+    font-weight: 700;
     border-radius: 8px;
     transition: filter 0.15s, box-shadow 0.15s;
     box-shadow: 0 2px 10px rgba(44,62,80,0.30);