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

org/cpp/dsa/2-d-dynamic-programming/0312-burst-balloons.org

@@ -0,0 +1,8 @@
+* TODO 0312. Burst Balloons :hard:
+:PROPERTIES:
+:NEETCODE: [[../../../../leetcode/out/roadmap.org::*0312. Burst Balloons][Roadmap]]
+:END:
+
+#+begin_src cpp
+
+#+end_src