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/0076-minimum-window-substring.org

@@ -1,18 +1,71 @@
 #+PROPERTY: STUDY_DECK_02
 * TODO 0076. Minimum Window Substring :hard:
 :PROPERTIES:
-:NEETCODE: [[file:../../roadmap.org::*0076. Minimum Window Substring][Roadmap]]
+:NEETCODE: [[file:../../roadmap.org::*0076. Minimum Window Substring][0076. Minimum Window Substring]]
 :END:
 
+Given two strings ~s~ and ~t~ of lengths ~m~ and ~n~ respectively, return /the *minimum window*/ */substring/*/ of /~s~/ such that every character in /~t~/ (*including duplicates*) is included in the window/. If there is no such substring, return /the empty string /~""~.
+
+The testcases will be generated such that the answer is *unique*.
+
+*Example 1:*
+
+
+#+begin_src
+Input: s = "ADOBECODEBANC", t = "ABC"
+Output: "BANC"
+Explanation: The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.
+#+end_src
+
+
+*Example 2:*
+
+
+#+begin_src
+Input: s = "a", t = "a"
+Output: "a"
+Explanation: The entire string s is the minimum window.
+#+end_src
+
+
+*Example 3:*
+
+
+#+begin_src
+Input: s = "a", t = "aa"
+Output: ""
+Explanation: Both 'a's from t must be included in the window.
+Since the largest window of s only has one 'a', return empty string.
+#+end_src
+
+
+*Constraints:*
+
+ - ~m == s.length~
+
+ - ~n == t.length~
+
+ - ~1 <= m, n <= 10^{5}~
+
+ - ~s~ and ~t~ consist of uppercase and lowercase English letters.
+
+*Follow up:* Could you find an algorithm that runs in ~O(m + n)~ time?
+
 ** TODO Approach
 Write your approach here.
 
 ** TODO Python
 #+begin_src python
-
+class Solution:
+    def minWindow(self, s: str, t: str) -> str:
 #+end_src
 
 ** TODO C++
 #+begin_src cpp
-
+class Solution {
+public:
+    string minWindow(string s, string t) {
+        
+    }
+};
 #+end_src