fix: preserve scroll position in cached grid views

display:none discards scrollTop in WebKitGTK, so navigating away
from album/artist/genre grids and back reset scroll to top.

Replace inline style.display toggling with a CSS class that uses
visibility:hidden + height:0 + overflow:hidden. This collapses
the element visually while keeping the DOM alive with its scroll
state intact. contain:strict on hidden views ensures zero layout
cost while collapsed.

frontend/index.css

@@ -152,3 +152,14 @@ body div.sidebar {
     height: 100%;
     contain: layout style paint;
 }
+
+/* Hidden cached views: use visibility+size collapse instead of
+   display:none so scroll containers preserve their scrollTop.
+   display:none discards scroll state in WebKitGTK. */
+.main-panel > .view-hidden {
+    visibility: hidden !important;
+    height: 0 !important;
+    overflow: hidden !important;
+    pointer-events: none !important;
+    contain: strict !important;
+}

frontend/index.ts

@@ -92,15 +92,16 @@ document.addEventListener('navigate', (e: Event) => {
             target = document.createElement(VIEW_TAGS[view]);
             viewCache.set(view, target);
             // Start hidden — we'll un-hide below
-            target.style.display = 'none';
+            target.classList.add('view-hidden');
             mainContent.appendChild(target);
         }
 
-        // Hide current, show target
+        // Hide current, show target.  Uses CSS class instead of
+        // display:none so scroll containers preserve scrollTop.
         if (currentViewEl && currentViewEl !== target) {
-            currentViewEl.style.display = 'none';
+            currentViewEl.classList.add('view-hidden');
         }
-        target.style.display = '';
+        target.classList.remove('view-hidden');
         currentViewEl = target;
         return;
     }
@@ -108,7 +109,7 @@ document.addEventListener('navigate', (e: Event) => {
     // --- Detail (ephemeral) views -----------------------------------------
     // Hide the current primary view
     if (currentViewEl) {
-        currentViewEl.style.display = 'none';
+        currentViewEl.classList.add('view-hidden');
     }
     // Remove any prior detail element
     if (currentDetailEl) {