docs(docs): add Approach diagrams and Explanation sections to LeetCode problem documentation

apps/docs/content/(tree)/235-lowest-common-ancestor-of-a-binary-search-tree.mdx

@@ -30,6 +30,22 @@ sidebar:
 - `p != q`
 - p and q will exist in the BST.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["lowestCommonAncestor(root, p, q)"]) --> I["cur = root"]
+  I --> W{"cur?"}
+  W -- no --> E(["fall off the loop — unreachable, p and q exist in the BST"])
+  W -- yes --> A{"p.val < cur.val and q.val < cur.val?"}
+  A -- yes --> L["cur = cur.left — both sit in the left subtree"]
+  L --> W
+  A -- no --> B{"p.val > cur.val and q.val > cur.val?"}
+  B -- yes --> R["cur = cur.right — both sit in the right subtree"]
+  R --> W
+  B -- no --> C(["return cur — the paths to p and q split here"])
+```
+
 ## Solution
 
 ```py
@@ -54,3 +70,7 @@ class Solution:
             else:
                 return cur
 ```
+
+## Explanation
+
+<YouTube id="gs2LMfuOR9k" title="Lowest Common Ancestor of a Binary Search Tree - Leetcode 235 - Python" />