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/bit-manipulation/0191-number-of-1-bits.org

@@ -1,18 +1,62 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0191. Number of 1 Bits :easy:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0191. Number of 1 Bits][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0191. Number of 1 Bits][0191. Number of 1 Bits]]
 :END:
 
+Given a positive integer ~n~, write a function that returns the number of set bits in its binary representation (also known as the Hamming weight).
+
+*Example 1:*
+
+*Input:* n = 11
+
+*Output:* 3
+
+*Explanation:*
+
+The input binary string *1011* has a total of three set bits.
+
+*Example 2:*
+
+*Input:* n = 128
+
+*Output:* 1
+
+*Explanation:*
+
+The input binary string *10000000* has a total of one set bit.
+
+*Example 3:*
+
+*Input:* n = 2147483645
+
+*Output:* 30
+
+*Explanation:*
+
+The input binary string *1111111111111111111111111111101* has a total of thirty set bits.
+
+*Constraints:*
+
+ - ~1 <= n <= 2^{31} - 1~
+
+*Follow up:* If this function is called many times, how would you optimize it?
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def hammingWeight(self, n: int) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int hammingWeight(int n) {
+        
+    }
+};
 #+end_src