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/intervals/0056-merge-intervals.org

@@ -1,18 +1,64 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0056. Merge Intervals :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0056. Merge Intervals][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0056. Merge Intervals][0056. Merge Intervals]]
 :END:
 
+Given an array of ~intervals~ where ~intervals[i] = [start_{i}, end_{i}]~, merge all overlapping intervals, and return /an array of the non-overlapping intervals that cover all the intervals in the input/.
+
+*Example 1:*
+
+
+#+begin_src
+Input: intervals = [[1,3],[2,6],[8,10],[15,18]]
+Output: [[1,6],[8,10],[15,18]]
+Explanation: Since intervals [1,3] and [2,6] overlap, merge them into [1,6].
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: intervals = [[1,4],[4,5]]
+Output: [[1,5]]
+Explanation: Intervals [1,4] and [4,5] are considered overlapping.
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: intervals = [[4,7],[1,4]]
+Output: [[1,7]]
+Explanation: Intervals [1,4] and [4,7] are considered overlapping.
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= intervals.length <= 10^{4}~
+
+ - ~intervals[i].length == 2~
+
+ - ~0 <= start_{i} <= end_{i} <= 10^{4}~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    vector<vector<int>> merge(vector<vector<int>>& intervals) {
+        
+    }
+};
 #+end_src