Add solution notes scaffold and sub-heading format

- roadmap.org: problems now have *** Python and *** C++ sub-headings,
  plus Notes: links to per-problem org files
- scaffold-notes.mjs: creates 199 note files in org/cpp/dsa/<topic>/
  with backlinks to roadmap.org
- 18 topic folders under org/cpp/dsa/ for NeetCode 150 problems
- Updated AGENTS.md with new conventions and workflow

leetcode/extract.mjs

@@ -207,10 +207,19 @@ function buildOrg(sortedNodes, problemsByTopic) {
   const difficultyTag = (d) =>
     d === "Easy" ? "easy" : d === "Medium" ? "medium" : "hard";
 
+  const topicSlug = (name) =>
+    name
+      .toLowerCase()
+      .replace(/[^a-z0-9]+/g, "-")
+      .replace(/(^-|-$)/g, "");
+
+  const notesRoot = "../../org/cpp/dsa";
+
   for (const node of sortedNodes) {
     const topicProblems = (problemsByTopic[node.name] || []).filter(
       (p) => p.neetcode150
     );
+    const slug = topicSlug(node.name);
     lines.push(`* TODO ${node.name} [/]`);
     lines.push("");
 
@@ -224,14 +233,18 @@ function buildOrg(sortedNodes, problemsByTopic) {
       const tag = difficultyTag(p.difficulty);
       const lcUrl = `${LEETCODE_BASE}${p.link}`;
       const num = p.code.split("-")[0];
+      const notesFile = `${notesRoot}/${slug}/${p.code}.org`;
       lines.push(`** TODO ${num}. ${p.name} :${tag}:`);
-      lines.push(`- Python: [[${GITHUB_SOLUTIONS}python/${p.code}.py][${p.code}.py]]`);
-      lines.push(`- C++: [[${GITHUB_SOLUTIONS}cpp/${p.code}.cpp][${p.code}.cpp]]`);
+      lines.push(`*** Python`);
+      lines.push(`- [[${GITHUB_SOLUTIONS}python/${p.code}.py][${p.code}.py]]`);
+      lines.push(`*** C++`);
+      lines.push(`- [[${GITHUB_SOLUTIONS}cpp/${p.code}.cpp][${p.code}.cpp]]`);
       lines.push(`- LeetCode: [[${lcUrl}][${p.link}]]`);
       if (p.video)
         lines.push(
           `- Video: [[https://youtube.com/watch?v=${p.video}][explanation]]`
         );
+      lines.push(`- Notes: [[${notesFile}][My Solution]]`);
     }
     lines.push("");
   }