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/0217-contains-duplicate.org

@@ -1,18 +1,58 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0217. Contains Duplicate :easy:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0217. Contains Duplicate][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0217. Contains Duplicate][0217. Contains Duplicate]]
 :END:
 
+Given an integer array ~nums~, return ~true~ if any value appears *at least twice* in the array, and return ~false~ if every element is distinct.
+
+*Example 1:*
+
+*Input:* nums = [1,2,3,1]
+
+*Output:* true
+
+*Explanation:*
+
+The element 1 occurs at the indices 0 and 3.
+
+*Example 2:*
+
+*Input:* nums = [1,2,3,4]
+
+*Output:* false
+
+*Explanation:*
+
+All elements are distinct.
+
+*Example 3:*
+
+*Input:* nums = [1,1,1,3,3,4,3,2,4,2]
+
+*Output:* true
+
+*Constraints:*
+
+ - ~1 <= nums.length <= 10^{5}~
+
+ - ~-10^{9} <= nums[i] <= 10^{9}~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    bool containsDuplicate(vector<int>& nums) {
+        
+    }
+};
 #+end_src