polish(ui): 侧栏可点块悬停/聚焦统一为主题色淡底

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/PostToc.tsx

@@ -73,14 +73,7 @@ export default function PostToc({ items }: { items: TocItem[] }) {
                 data-toc-id={it.id}
                 href={`#${it.id}`}
                 onClick={jump(it.id)}
-                className="block py-1.5 pr-1 text-[12.5px] leading-snug transition-colors"
-                style={{
-                  paddingLeft: it.level === 3 ? 20 : 12,
-                  marginLeft: -1,
-                  borderLeft: `2px solid ${isActive ? "var(--accent)" : "transparent"}`,
-                  color: isActive ? "var(--accent)" : "var(--ink-2)",
-                  fontWeight: isActive ? 600 : 400,
-                }}
+                className={`j13-toc-link${it.level === 3 ? " is-h3" : ""}${isActive ? " is-active" : ""}`}
               >
                 {it.text}
               </a>