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/0091-decode-ways.org

@@ -1,18 +1,88 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0091. Decode Ways :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0091. Decode Ways][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0091. Decode Ways][0091. Decode Ways]]
 :END:
 
+You have intercepted a secret message encoded as a string of numbers. The message is *decoded* via the following mapping:
+
+~"1" -> 'A'
+
+"2" -> 'B'
+
+...
+
+"25" -> 'Y'
+
+"26" -> 'Z'~
+
+However, while decoding the message, you realize that there are many different ways you can decode the message because some codes are contained in other codes (~"2"~ and ~"5"~ vs ~"25"~).
+
+For example, ~"11106"~ can be decoded into:
+
+ - ~"AAJF"~ with the grouping ~(1, 1, 10, 6)~
+
+ - ~"KJF"~ with the grouping ~(11, 10, 6)~
+
+ - The grouping ~(1, 11, 06)~ is invalid because ~"06"~ is not a valid code (only ~"6"~ is valid).
+
+Note: there may be strings that are impossible to decode.
+
+Given a string s containing only digits, return the *number of ways* to *decode* it. If the entire string cannot be decoded in any valid way, return ~0~.
+
+The test cases are generated so that the answer fits in a *32-bit* integer.
+
+*Example 1:*
+
+*Input:* s = "12"
+
+*Output:* 2
+
+*Explanation:*
+
+"12" could be decoded as "AB" (1 2) or "L" (12).
+
+*Example 2:*
+
+*Input:* s = "226"
+
+*Output:* 3
+
+*Explanation:*
+
+"226" could be decoded as "BZ" (2 26), "VF" (22 6), or "BBF" (2 2 6).
+
+*Example 3:*
+
+*Input:* s = "06"
+
+*Output:* 0
+
+*Explanation:*
+
+"06" cannot be mapped to "F" because of the leading zero ("6" is different from "06"). In this case, the string is not a valid encoding, so return 0.
+
+*Constraints:*
+
+ - ~1 <= s.length <= 100~
+
+ - ~s~ contains only digits and may contain leading zero(s).
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def numDecodings(self, s: str) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int numDecodings(string s) {
+        
+    }
+};
 #+end_src