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/1-d-dynamic-programming/0005-longest-palindromic-substring.org

@@ -1,18 +1,51 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0005. Longest Palindromic Substring :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0005. Longest Palindromic Substring][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0005. Longest Palindromic Substring][0005. Longest Palindromic Substring]]
 :END:
 
+Given a string ~s~, return /the longest/ /palindromic/ /substring/ in ~s~.
+
+*Example 1:*
+
+
+#+begin_src
+Input: s = "babad"
+Output: "bab"
+Explanation: "aba" is also a valid answer.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: s = "cbbd"
+Output: "bb"
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= s.length <= 1000~
+
+ - ~s~ consist of only digits and English letters.
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def longestPalindrome(self, s: str) -> str:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    string longestPalindrome(string s) {
+        
+    }
+};
 #+end_src