fix: consolidate reader-nav-thumb active/hover CSS rules

Remove duplicate .reader-nav-thumb:hover and .reader-nav-thumb.active
blocks from the old sidebar styles. The newer rules using opacity and
border-left (added ~line 2646) supersede them.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/static/style.css

@@ -2547,14 +2547,6 @@ body.select-mode .gallery-infinite-container {
   transition: all 0.2s ease;
 }
 
-.reader-nav-thumb:hover {
-  border-color: rgba(255, 255, 255, 0.3);
-}
-
-.reader-nav-thumb.active {
-  border-color: var(--btn-primary);
-}
-
 .reader-nav-thumb img {
   width: 100%;
   height: auto;