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/math-geometry/0009-palindrome-number.org

@@ -1,18 +1,62 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0009. Palindrome Number :easy:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0009. Palindrome Number][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0009. Palindrome Number][0009. Palindrome Number]]
 :END:
 
+Given an integer ~x~, return ~true~/ if /~x~/ is a //*palindrome*//, and /~false~/ otherwise/.
+
+*Example 1:*
+
+
+#+begin_src
+Input: x = 121
+Output: true
+Explanation: 121 reads as 121 from left to right and from right to left.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: x = -121
+Output: false
+Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: x = 10
+Output: false
+Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
+#+end_src
+
+
+*Constraints:*
+
+ - ~-2^{31} <= x <= 2^{31} - 1~
+
+*Follow up:* Could you solve it without converting the integer to a string?
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def isPalindrome(self, x: int) -> bool:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    bool isPalindrome(int x) {
+        
+    }
+};
 #+end_src