e2e: parse codex rollout session id as JSON, not regex

TestCodexResumeRestoredSessionWithSanitizedCompactedHistory failed every run on main: readCodexSessionID anchored a regex on the session_meta line's field order, which Codex changed in 0.142.x, so it matched nothing ("session_meta id not found in rollout"). The CLI parses the same file fine via JSON. Decode the rollout line-by-line and read payload.id the same way, so the test survives future Codex field reordering.