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/1220-count-vowels-permutation.org

@@ -1,18 +1,73 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 1220. Count Vowels Permutation :hard:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*1220. Count Vowels Permutation][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*1220. Count Vowels Permutation][1220. Count Vowels Permutation]]
 :END:
 
+Given an integer ~n~, your task is to count how many strings of length ~n~ can be formed under the following rules:
+
+ - Each character is a lower case vowel (~'a'~, ~'e'~, ~'i'~, ~'o'~, ~'u'~)
+
+ - Each vowel ~'a'~ may only be followed by an ~'e'~.
+
+ - Each vowel ~'e'~ may only be followed by an ~'a'~ or an ~'i'~.
+
+ - Each vowel ~'i'~ *may not* be followed by another ~'i'~.
+
+ - Each vowel ~'o'~ may only be followed by an ~'i'~ or a ~'u'~.
+
+ - Each vowel ~'u'~ may only be followed by an ~'a'~.
+
+Since the answer may be too large, return it modulo ~10^9 + 7~.
+
+*Example 1:*
+
+
+#+begin_src
+Input: n = 1
+Output: 5
+Explanation: All possible strings are: "a", "e", "i" , "o" and "u".
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: n = 2
+Output: 10
+Explanation: All possible strings are: "ae", "ea", "ei", "ia", "ie", "io", "iu", "oi", "ou" and "ua".
+#+end_src
+
+
+*Example 3: *
+
+
+#+begin_src
+Input: n = 5
+Output: 68
+#+end_src
+
+
+*Constraints:*
+
+ - ~1 <= n <= 2 * 10^4~
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def countVowelPermutation(self, n: int) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int countVowelPermutation(int n) {
+        
+    }
+};
 #+end_src