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/stack/0150-evaluate-reverse-polish-notation.org

@@ -1,18 +1,84 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0150. Evaluate Reverse Polish Notation :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0150. Evaluate Reverse Polish Notation][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0150. Evaluate Reverse Polish Notation][0150. Evaluate Reverse Polish Notation]]
 :END:
 
+You are given an array of strings ~tokens~ that represents an arithmetic expression in a Reverse Polish Notation.
+
+Evaluate the expression. Return /an integer that represents the value of the expression/.
+
+*Note* that:
+
+ - The valid operators are ~'+'~, ~'-'~, ~'*'~, and ~'/'~.
+
+ - Each operand may be an integer or another expression.
+
+ - The division between two integers always *truncates toward zero*.
+
+ - There will not be any division by zero.
+
+ - The input represents a valid arithmetic expression in a reverse polish notation.
+
+ - The answer and all the intermediate calculations can be represented in a *32-bit* integer.
+
+*Example 1:*
+
+
+#+begin_src
+Input: tokens = ["2","1","+","3","*"]
+Output: 9
+Explanation: ((2 + 1) * 3) = 9
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: tokens = ["4","13","5","/","+"]
+Output: 6
+Explanation: (4 + (13 / 5)) = 6
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
+Output: 22
+Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
+= ((10 * (6 / (12 * -11))) + 17) + 5
+= ((10 * (6 / -132)) + 17) + 5
+= ((10 * 0) + 17) + 5
+= (0 + 17) + 5
+= 17 + 5
+= 22
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= tokens.length <= 10^{4}~
+
+ - ~tokens[i]~ is either an operator: ~"+"~, ~"-"~, ~"*"~, or ~"/"~, or an integer in the range ~[-200, 200]~.
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def evalRPN(self, tokens: List[str]) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int evalRPN(vector<string>& tokens) {
+        
+    }
+};
 #+end_src