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/sliding-window/0003-longest-substring-without-repeating-characters.org

@@ -1,18 +1,63 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0003. Longest Substring Without Repeating Characters :medium:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0003. Longest Substring Without Repeating Characters][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0003. Longest Substring Without Repeating Characters][0003. Longest Substring Without Repeating Characters]]
 :END:
 
+Given a string ~s~, find the length of the *longest* *substring* without duplicate characters.
+
+*Example 1:*
+
+
+#+begin_src
+Input: s = "abcabcbb"
+Output: 3
+Explanation: The answer is "abc", with the length of 3. Note that "bca" and "cab" are also correct answers.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: s = "bbbbb"
+Output: 1
+Explanation: The answer is "b", with the length of 1.
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: s = "pwwkew"
+Output: 3
+Explanation: The answer is "wke", with the length of 3.
+Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.
+#+end_src
+
+
+*Constraints:*
+
+ - ~0 <= s.length <= 5 * 10^{4}~
+
+ - ~s~ consists of English letters, digits, symbols and spaces.
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    int lengthOfLongestSubstring(string s) {
+        
+    }
+};
 #+end_src