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/stack/0084-largest-rectangle-in-histogram.org

@@ -1,18 +1,52 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0084. Largest Rectangle In Histogram :hard:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0084. Largest Rectangle In Histogram][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0084. Largest Rectangle In Histogram][0084. Largest Rectangle In Histogram]]
 :END:
 
+Given an array of integers ~heights~ representing the histogram's bar height where the width of each bar is ~1~, return /the area of the largest rectangle in the histogram/.
+
+*Example 1:*
+
+
+#+begin_src
+Input: heights = [2,1,5,6,2,3]
+Output: 10
+Explanation: The above is a histogram where width of each bar is 1.
+The largest rectangle is shown in the red area, which has an area = 10 units.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: heights = [2,4]
+Output: 4
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= heights.length <= 10^{5}~
+
+ - ~0 <= heights[i] <= 10^{4}~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def largestRectangleArea(self, heights: List[int]) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int largestRectangleArea(vector<int>& heights) {
+        
+    }
+};
 #+end_src