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

apps/docs/content/(tree)/236-lowest-common-ancestor-of-a-binary-tree.mdx

@@ -30,6 +30,21 @@ sidebar:
 - `p != q`
 - p and q will exist in the tree.
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["lowestCommonAncestor(root, p, q)"]) --> B{"not root?"}
+  B -- yes --> N(["return None"])
+  B -- no --> M{"root == p or root == q?"}
+  M -- yes --> R(["return root — a node is its own ancestor"])
+  M -- no --> L["l = self.lowestCommonAncestor(root.left, p, q)"]
+  L --> Q["r = self.lowestCommonAncestor(root.right, p, q)"]
+  Q --> D{"l and r?"}
+  D -- yes --> A(["return root — p and q were found on different sides"])
+  D -- no --> E(["return l or r — pass up whichever side found something"])
+```
+
 ## Solution
 
 ```py