docs(docs): add page icon frontmatter to problem pages

apps/docs/content/(03-hierarchical)/tree-bfs/102-binary-tree-level-order-traversal.mdx

@@ -1,6 +1,7 @@
 ---
 title: '102. Binary Tree Level Order Traversal'
 description: Given the root of a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, level by level)
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Binary Tree Level Order Traversal'
   badge: 'Medium'

apps/docs/content/(03-hierarchical)/tree-bfs/1448-count-good-nodes-in-binary-tree.mdx

@@ -1,6 +1,7 @@
 ---
 title: '1448. Count Good Nodes in Binary Tree'
 description: Given a binary tree root, a node X in the tree is named good if in the path from root to X there are no nodes with a value greater than X
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Count Good Nodes in Binary Tree'
   badge: 'Medium'

apps/docs/content/(03-hierarchical)/tree-bfs/199-binary-tree-right-side-view.mdx

@@ -1,6 +1,7 @@
 ---
 title: '199. Binary Tree Right Side View'
 description: Given the root of a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom
+icon: line-dot-left-horizontal
 sidebar:
   label: 'Binary Tree Right Side View'
   badge: 'Medium'