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/0077-combinations.org

@@ -1,18 +1,55 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0077. Combinations :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0077. Combinations][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0077. Combinations][0077. Combinations]]
 :END:
 
+Given two integers ~n~ and ~k~, return /all possible combinations of/ ~k~ /numbers chosen from the range/ ~[1, n]~.
+
+You may return the answer in *any order*.
+
+*Example 1:*
+
+
+#+begin_src
+Input: n = 4, k = 2
+Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
+Explanation: There are 4 choose 2 = 6 total combinations.
+Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: n = 1, k = 1
+Output: [[1]]
+Explanation: There is 1 choose 1 = 1 total combination.
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= n <= 20~
+
+ - ~1 <= k <= n~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def combine(self, n: int, k: int) -> List[List[int]]:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    vector<vector<int>> combine(int n, int k) {
+        
+    }
+};
 #+end_src