Keep only open work in docs/TODO.md (closes #440)

Removed the Completed Steps section and the history in Next Step.
Workflow step 3 now says to delete Next Step, as the standard Workflow
section does. Next Step points to the open bugs that block the release.

Model: opus-5-5

docs/TODO.md

@@ -2,7 +2,7 @@
 
 - branch (from `main`)
 - do the work in Next Step
-- move Next Step to the top of Completed Steps
+- delete Next Step from `TODO.md`
 - move the top item of Future Steps into Next Step
 - commit (`TODO.md` changes in the same commit as the work)
 - merge to `main` if the branch is not protected, otherwise open a PR
@@ -14,7 +14,8 @@ pre-1.0
 
 # Next Step
 
-None for an agent. Merging `next` into `main` is the owner's.
+Fix the open bugs on the issue tracker that block the release. Merging `next`
+into `main` is the owner's.
 
 # Future Steps