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/arrays-hashing/0036-valid-sudoku.org

@@ -1,18 +1,83 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0036. Valid Sudoku :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0036. Valid Sudoku][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0036. Valid Sudoku][0036. Valid Sudoku]]
 :END:
 
+Determine if a ~9 x 9~ Sudoku board is valid. Only the filled cells need to be validated *according to the following rules*:
+
+ - Each row must contain the digits ~1-9~ without repetition.
+
+ - Each column must contain the digits ~1-9~ without repetition.
+
+ - Each of the nine ~3 x 3~ sub-boxes of the grid must contain the digits ~1-9~ without repetition.
+
+*Note:*
+
+ - A Sudoku board (partially filled) could be valid but is not necessarily solvable.
+
+ - Only the filled cells need to be validated according to the mentioned rules.
+
+*Example 1:*
+
+
+#+begin_src
+Input: board = 
+[["5","3",".",".","7",".",".",".","."]
+,["6",".",".","1","9","5",".",".","."]
+,[".","9","8",".",".",".",".","6","."]
+,["8",".",".",".","6",".",".",".","3"]
+,["4",".",".","8",".","3",".",".","1"]
+,["7",".",".",".","2",".",".",".","6"]
+,[".","6",".",".",".",".","2","8","."]
+,[".",".",".","4","1","9",".",".","5"]
+,[".",".",".",".","8",".",".","7","9"]]
+Output: true
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: board = 
+[["8","3",".",".","7",".",".",".","."]
+,["6",".",".","1","9","5",".",".","."]
+,[".","9","8",".",".",".",".","6","."]
+,["8",".",".",".","6",".",".",".","3"]
+,["4",".",".","8",".","3",".",".","1"]
+,["7",".",".",".","2",".",".",".","6"]
+,[".","6",".",".",".",".","2","8","."]
+,[".",".",".","4","1","9",".",".","5"]
+,[".",".",".",".","8",".",".","7","9"]]
+Output: false
+Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.
+#+end_src
+
+
+*Constraints:*
+
+ - ~board.length == 9~
+
+ - ~board[i].length == 9~
+
+ - ~board[i][j]~ is a digit ~1-9~ or ~'.'~.
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def isValidSudoku(self, board: List[List[str]]) -> bool:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    bool isValidSudoku(vector<vector<char>>& board) {
+        
+    }
+};
 #+end_src