Migrate a suite to e2e

A migration is never one change. Each session ports one slice, proves it, and leaves both suites green: the old runner keeps every test it had, and the new e2e tests pass beside it. A progress file, MIGRATION.md, records what moved, what is left, and why, so the next session, yours or another agent's, starts from it instead of from scratch. The user decides when an old test goes.

Two references do most of the work. Read them; do not restate them.