feat: add superderive child and open phase-2 routing

Attach the stepwise derivation toolkit as a submodule and default
SUPERPAPER_PHASE to 2 so rewrite-figure can use superderive. Notes
still keep align for short expansions without cancel or subst.

examples/derive-delegate/outline.md

@@ -0,0 +1,14 @@
+# Outline: Scaled attention
+
+## Lecture map
+
+| file | lecture_title | paper_sections | ledger_ids |
+|---|---|---|---|
+| sec-01.tex | 这篇论文在问什么 | 1 | Q1 |
+| sec-02.tex | 主张与贡献 | 1 | C1, F3 |
+| sec-03.tex | 总结与延伸 | 1 | C1 |
+| sec-app-a.tex | 符号表 | — | |
+
+## Locked
+- 首节标题必须是「这篇论文在问什么」
+- 末节（appendix 前）必须是「总结与延伸」