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/arrays-hashing/0049-group-anagrams.org

@@ -1,18 +1,60 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0049. Group Anagrams :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0049. Group Anagrams][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0049. Group Anagrams][0049. Group Anagrams]]
 :END:
 
+Given an array of strings ~strs~, group the anagrams together. You can return the answer in *any order*.
+
+*Example 1:*
+
+*Input:* strs = ["eat","tea","tan","ate","nat","bat"]
+
+*Output:* [["bat"],["nat","tan"],["ate","eat","tea"]]
+
+*Explanation:*
+
+ - There is no string in strs that can be rearranged to form ~"bat"~.
+
+ - The strings ~"nat"~ and ~"tan"~ are anagrams as they can be rearranged to form each other.
+
+ - The strings ~"ate"~, ~"eat"~, and ~"tea"~ are anagrams as they can be rearranged to form each other.
+
+*Example 2:*
+
+*Input:* strs = [""]
+
+*Output:* [[""]]
+
+*Example 3:*
+
+*Input:* strs = ["a"]
+
+*Output:* [["a"]]
+
+*Constraints:*
+
+ - ~1 <= strs.length <= 10^{4}~
+
+ - ~0 <= strs[i].length <= 100~
+
+ - ~strs[i]~ consists of lowercase English letters.
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    vector<vector<string>> groupAnagrams(vector<string>& strs) {
+        
+    }
+};
 #+end_src