docs(docs): add Approach and Explanation sections with mermaid diagrams to problem pages

apps/docs/content/(array)/35-search-insert-position.mdx

@@ -31,6 +31,22 @@ You must write an algorithm with O(log n) runtime complexity.
 - `nums` contains distinct values sorted in ascending order.
 - `-10^4 <= target <= 10^4`
 
+## Approach
+
+```mermaid
+flowchart TD
+  S(["searchInsert(nums, target)"]) --> I["l = 0, r = n - 1"]
+  I --> W{"l <= r?"}
+  W -- yes --> M["m = (l + r) // 2"]
+  M --> Q{"nums[m] vs target"}
+  Q -- equal --> R(["return m"])
+  Q -- "nums[m] < target" --> L["l = m + 1"]
+  L --> W
+  Q -- "nums[m] > target" --> H["r = m - 1"]
+  H --> W
+  W -- no --> E(["return (l + r) // 2 + 1 — the insert slot"])
+```
+
 ## Solution
 
 ```py
@@ -49,3 +65,7 @@ class Solution:
 
         return (l + r) // 2 + 1
 ```
+
+## Explanation
+
+<YouTube id="K-RYzDZkzCI" title="Search Insert Position - Binary Search - Leetcode 35 - Python" />