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/backtracking/0040-combination-sum-ii.org

@@ -1,18 +1,66 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0040. Combination Sum II :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0040. Combination Sum II][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0040. Combination Sum II][0040. Combination Sum II]]
 :END:
 
+Given a collection of candidate numbers (~candidates~) and a target number (~target~), find all unique combinations in ~candidates~ where the candidate numbers sum to ~target~.
+
+Each number in ~candidates~ may only be used *once* in the combination.
+
+*Note:* The solution set must not contain duplicate combinations.
+
+*Example 1:*
+
+
+#+begin_src
+Input: candidates = [10,1,2,7,6,1,5], target = 8
+Output: 
+[
+[1,1,6],
+[1,2,5],
+[1,7],
+[2,6]
+]
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: candidates = [2,5,2,1,2], target = 5
+Output: 
+[
+[1,2,2],
+[5]
+]
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= candidates.length <= 100~
+
+ - ~1 <= candidates[i] <= 50~
+
+ - ~1 <= target <= 30~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def combinationSum2(self, candidates: List[int], target: int) -> List[List[int]]:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    vector<vector<int>> combinationSum2(vector<int>& candidates, int target) {
+        
+    }
+};
 #+end_src