docs: replace legacy line‑dot‑left‑horizontal icons with unified dot icon across docs

apps/docs/content/(04-relational)/graph-dfs/200-number-of-islands.mdx

@@ -1,7 +1,7 @@
 ---
 title: '200. Number of Islands'
 description: Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands
-icon: line-dot-left-horizontal
+icon: dot
 sidebar:
   label: 'Number of Islands'
   badge: 'Medium'