new: scaffold materializes a schema default only for a required field

Files changed:
- CHANGES.md
- VERSION
- instructions/CONTRACT.md
- tools/CONTRACT.md
- tools/chemenu/commands/new_page.py
- tools/chemenu/tests/test_new_page.py
- types/type-spec.md

instructions/CONTRACT.md

@@ -89,6 +89,11 @@ produces; `migration_kind:` (`mechanical` | `assisted`); and `obligation:`
 (`required` | `offered`, default `required`). It lives at
 `instructions/migrations/<version>-<slug>.md`.
 
+`wikitool new instruction` scaffolds none of the three: `migrates_to:` and `migration_kind:`
+have no schema `default:` at all, and an ordinary instruction's scaffold no longer materializes
+`obligation:`'s default either - all three are added by hand when a migration document is
+written, per [migrate-corpus.md](migrate-corpus.md).
+
 `migration_kind:` and `obligation:` are **two axes, not one**. The first says how the work is
 carried out, the second whether it has to happen at all: