Redesign home page layout and improve user experience

Replaced the old card-based layout in `Index.razor` with a modern, visually appealing home page design. Added a hero header, content section, and call-to-action button for signing documents. Introduced new SVG icons and text elements to enhance the UI.

Removed the `OnAfterRenderAsync` method and automatic redirection logic to simplify user navigation. Added a new stylesheet link for the DevExpress Blazor theme.

Updated `app.css` to support the new design:
- Changed `article` overflow to `overflow-y: auto`.
- Added new classes for layout, buttons, and feature badges.
- Styled the home page with a gradient background, rounded corners, and hover effects.

These changes improve usability, responsiveness, and visual consistency.

EnvelopeGenerator.ReceiverUI/wwwroot/css/app.css

@@ -14,7 +14,7 @@ article {
     height: calc(100vh - 36px);
     display: flex;
     flex-direction: column;
-    overflow: hidden;
+    overflow-y: auto;
     padding-left: 0 !important;
     padding-right: 0 !important;
 }
@@ -244,6 +244,87 @@ article {
     flex-wrap: wrap;
 }
 
+/* ── Home page ───────────────────────────────────────────────────────────── */
+.home-page-wrapper {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    min-height: calc(100vh - 36px);
+    background: linear-gradient(160deg, #1e2e3e 0%, #2c3e50 40%, #3498db 100%);
+    padding-bottom: 36px;
+}
+
+.home-hero-header {
+    width: 100%;
+    padding: 48px 24px 36px;
+    text-align: center;
+}
+
+.home-hero-header__inner {
+    display: inline-flex;
+    align-items: center;
+    gap: 20px;
+    color: #fff;
+}
+
+.home-hero-header__icon {
+    opacity: 0.90;
+    flex-shrink: 0;
+}
+
+.home-hero-header__title {
+    font-size: 2rem;
+    font-weight: 700;
+    margin: 0;
+    color: #fff;
+    letter-spacing: 0.02em;
+}
+
+.home-hero-header__subtitle {
+    font-size: 0.92rem;
+    margin: 4px 0 0;
+    color: rgba(255,255,255,0.75);
+}
+
+.home-content {
+    width: 100%;
+    max-width: 520px;
+    padding: 0 16px;
+}
+
+.home-card {
+    border-radius: 12px !important;
+    overflow: hidden;
+}
+
+.home-btn-primary {
+    background: linear-gradient(135deg, #2c3e50 0%, #3498db 100%);
+    border: none;
+    color: #fff;
+    font-weight: 500;
+    border-radius: 8px;
+    transition: filter 0.15s, box-shadow 0.15s;
+    box-shadow: 0 2px 10px rgba(44,62,80,0.30);
+}
+
+.home-btn-primary:hover {
+    filter: brightness(1.12);
+    box-shadow: 0 4px 16px rgba(44,62,80,0.40);
+    color: #fff;
+}
+
+.home-feature-badge {
+    display: inline-flex;
+    align-items: center;
+    background: rgba(52,152,219,0.10);
+    color: #3498db;
+    border: 1px solid rgba(52,152,219,0.25);
+    border-radius: 20px;
+    padding: 4px 12px;
+    font-size: 0.75rem;
+    font-weight: 500;
+}
+
 /* ── Footer ──────────────────────────────────────────────────────────────── */
 .receiver-footer {
     position: fixed;