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/AGENTS.md

@@ -68,9 +68,28 @@ Arrays & Hashing
 ## Org-Mode Format
 
 Each topic is a `* TODO` heading with a `[/]` cookie for progress.
-Problems are `- [ ] TODO` items with difficulty tags (`:easy:`,
-`:medium:`, `:hard:`). Python and C++ solution links are nested
-`- [ ] TODO` sub-items. LeetCode and video links are plain list items.
+Problems are `** TODO` sub-headings with difficulty tags (`:easy:`,
+`:medium:`, `:hard:`). Python and C++ solution links are `***` sub-headings
+under each problem. Each problem also links to a notes file at
+`org/cpp/dsa/<topic>/<problem>.org` for personal solutions and flashcards.
+
+### Notes Files
+
+`org/cpp/dsa/<topic>/<code>.org` — one per NeetCode 150 problem (199 total).
+Scaffolded by `scaffold-notes.mjs`. Template:
+
+```org
+* TODO 0217. Contains Duplicate :easy:
+:PROPERTIES:
+:NEETCODE: [[../../../../leetcode/out/roadmap.org::*0217. Contains Duplicate][Roadmap]]
+:END:
+
+#+begin_src cpp
+
+#+end_src
+```
+
+Run `node scaffold-notes.mjs` to create missing note files (skips existing).
 
 ## Updating