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/2-d-dynamic-programming/0518-coin-change-ii.org

@@ -1,18 +1,75 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0518. Coin Change II :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0518. Coin Change II][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0518. Coin Change II][0518. Coin Change II]]
 :END:
 
+You are given an integer array ~coins~ representing coins of different denominations and an integer ~amount~ representing a total amount of money.
+
+Return /the number of combinations that make up that amount/. If that amount of money cannot be made up by any combination of the coins, return ~0~.
+
+You may assume that you have an infinite number of each kind of coin.
+
+The answer is *guaranteed* to fit into a signed *32-bit* integer.
+
+*Example 1:*
+
+
+#+begin_src
+Input: amount = 5, coins = [1,2,5]
+Output: 4
+Explanation: there are four ways to make up the amount:
+5=5
+5=2+2+1
+5=2+1+1+1
+5=1+1+1+1+1
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: amount = 3, coins = [2]
+Output: 0
+Explanation: the amount of 3 cannot be made up just with coins of 2.
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: amount = 10, coins = [10]
+Output: 1
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= coins.length <= 300~
+
+ - ~1 <= coins[i] <= 5000~
+
+ - All the values of ~coins~ are *unique*.
+
+ - ~0 <= amount <= 5000~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def change(self, amount: int, coins: List[int]) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int change(int amount, vector<int>& coins) {
+        
+    }
+};
 #+end_src