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/greedy/0978-longest-turbulent-subarray.org

@@ -1,18 +1,76 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0978. Longest Turbulent Subarray :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0978. Longest Turbulent Subarray][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0978. Longest Turbulent Subarray][0978. Longest Turbulent Subarray]]
 :END:
 
+Given an integer array ~arr~, return /the length of a maximum size turbulent subarray of/ ~arr~.
+
+A subarray is *turbulent* if the comparison sign flips between each adjacent pair of elements in the subarray.
+
+More formally, a subarray ~[arr[i], arr[i + 1], ..., arr[j]]~ of ~arr~ is said to be turbulent if and only if:
+
+ - For ~i <= k < j~:
+
+ - ~arr[k] > arr[k + 1]~ when ~k~ is odd, and
+
+ - ~arr[k] < arr[k + 1]~ when ~k~ is even.
+
+ - Or, for ~i <= k < j~:
+ 
+ - ~arr[k] > arr[k + 1]~ when ~k~ is even, and
+
+ - ~arr[k] < arr[k + 1]~ when ~k~ is odd.
+
+*Example 1:*
+
+
+#+begin_src
+Input: arr = [9,4,2,10,7,8,8,1,9]
+Output: 5
+Explanation: arr[1] > arr[2] < arr[3] > arr[4] < arr[5]
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: arr = [4,8,12,16]
+Output: 2
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: arr = [100]
+Output: 1
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= arr.length <= 4 * 10^{4}~
+
+ - ~0 <= arr[i] <= 10^{9}~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def maxTurbulenceSize(self, arr: List[int]) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int maxTurbulenceSize(vector<int>& arr) {
+        
+    }
+};
 #+end_src