P3: Simplify AutoFlow release: reduce git branch/tag dance, avoid force-push

## What to build

`tools/autoflow/release.ts:248-317` performs complex branch merges, checkouts, and force-pushes tags. Simplify the release plan to reduce the risk of a half-released state.

## Acceptance criteria

- [ ] Fewer branch transitions.
- [ ] No force-push of tags unless truly necessary and guarded.
- [ ] Release still works and tests pass.

## Blocked by

#294