feat: populate note files with problem descriptions and code stubs

Add populate-notes.mjs that fetches problem descriptions and
Python/C++ code stubs from LeetCode's GraphQL API. Populated
all 197 NeetCode 150 note files with:
- Problem description (examples, constraints)
- Python code stub (function signature)
- C++ code stub (function signature + includes)

API responses cached in leetcode/.cache/leetcode/ for instant re-runs.

org/study_deck_02/dsa/sliding-window/0239-sliding-window-maximum.org

@@ -1,18 +1,63 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0239. Sliding Window Maximum :hard:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0239. Sliding Window Maximum][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0239. Sliding Window Maximum][0239. Sliding Window Maximum]]
 :END:
 
+You are given an array of integers ~nums~, there is a sliding window of size ~k~ which is moving from the very left of the array to the very right. You can only see the ~k~ numbers in the window. Each time the sliding window moves right by one position.
+
+Return /the max sliding window/.
+
+*Example 1:*
+
+
+#+begin_src
+Input: nums = [1,3,-1,-3,5,3,6,7], k = 3
+Output: [3,3,5,5,6,7]
+Explanation: 
+Window position                Max
+---------------               -----
+[1  3  -1] -3  5  3  6  7       3
+ 1 [3  -1  -3] 5  3  6  7       3
+ 1  3 [-1  -3  5] 3  6  7       5
+ 1  3  -1 [-3  5  3] 6  7       5
+ 1  3  -1  -3 [5  3  6] 7       6
+ 1  3  -1  -3  5 [3  6  7]      7
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: nums = [1], k = 1
+Output: [1]
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= nums.length <= 10^{5}~
+
+ - ~-10^{4} <= nums[i] <= 10^{4}~
+
+ - ~1 <= k <= nums.length~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def maxSlidingWindow(self, nums: List[int], k: int) -> List[int]:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
+        
+    }
+};
 #+end_src