Remove obsolete sponsor styles

src/serena/resources/dashboard/dashboard.css

@@ -255,93 +255,6 @@ body {
     object-fit: contain;
 }
 
-.sponsor-nav-btn {
-    position: absolute;
-    background-color: transparent;
-    color: var(--text-muted);
-    border: none;
-    font-size: 28px;
-    cursor: pointer;
-    padding: 8px 12px;
-    transition: color 0.3s ease;
-    z-index: 10;
-    user-select: none;
-    opacity: 0.4;
-}
-
-.sponsor-nav-btn:hover {
-    color: var(--text-primary);
-    opacity: 0.7;
-}
-
-.sponsor-nav-btn:active {
-    color: var(--btn-primary);
-}
-
-.platinum-sponsors-section .sponsor-nav-left {
-    left: 5px;
-}
-
-.platinum-sponsors-section .sponsor-nav-right {
-    right: 5px;
-}
-
-.gold-sponsors-section .sponsor-nav-btn {
-    font-size: 24px;
-}
-
-.gold-sponsors-section .sponsor-nav-left {
-    left: 5px;
-}
-
-.gold-sponsors-section .sponsor-nav-right {
-    right: 5px;
-}
-
-/* Responsive adjustments for sponsors */
-@media (max-width: 768px) {
-    .platinum-sponsor-slide .sponsor-content {
-        font-size: 28px;
-        padding: 10px;
-    }
-
-    .header-sponsor .platinum-sponsor-slide .sponsor-content {
-        font-size: 18px;
-    }
-
-    .gold-sponsor-slide .sponsor-content {
-        font-size: 14px;
-        padding: 8px 10px;
-    }
-
-    .sponsor-nav-btn {
-        font-size: 22px;
-        padding: 5px 8px;
-    }
-
-    .gold-sponsors-section .sponsor-nav-btn {
-        font-size: 20px;
-    }
-
-    .header {
-        flex-wrap: wrap;
-        min-height: auto;
-    }
-
-    .header-nav {
-        order: 2;
-    }
-
-    .logo-container {
-        order: 1;
-    }
-
-    .header-sponsor {
-        order: 2;
-        width: 100%;
-        margin-top: 10px;
-    }
-}
 .page-view {
     max-width: 1600px;
     margin: 0 auto;