TODO.md workflow: branch from and merge into next (closes #137)

The "Workflow" list said to branch from main and to merge to main or open a
pull request. It now says to branch from next, open a pull request that
targets next, that the repository manager squash-merges a reviewed pull
request into next, and that only sneak merges next into main, as the README
does. The other items are unchanged. Docs only.

Model: opus-5-5

TODO.md

@@ -1,12 +1,15 @@
 # Workflow
 
-- branch (from `main`)
+- branch from `next`
 - do the work in Next Step
 - move Next Step to the top of Completed Steps
 - 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
 - push
+- open a pull request that targets `next`
+- once the pull request has passed review, the repository manager squash-merges
+  it into `next`
+- only sneak merges `next` into `main`
 
 # Status
 
@@ -22,6 +25,11 @@ declares one.
 
 # Completed Steps
 
+- 2026-09-29: The "Workflow" list at the top of this file now says to branch
+  from `next` and open a pull request that targets `next`, that the repository
+  manager squash-merges a reviewed pull request into `next`, and that only sneak
+  merges `next` into `main`, as the README does (issue 137).
+
 - 2026-09-29: The README's "Development workflow" and "For LLMs" sections now
   say work branches from `next`, every pull request targets `next`, the
   repository manager squash-merges reviewed pull requests into `next`, and only