feat(trial): LES-1184 7-day trial retention (PR-A1~A5)
See issue 420221d2 / LES-1184 for full design. 12 commits: PR-A1 scaffold → A5 Portal cancel fallback. Reviewer Opus 4.7 已 sign-off。需要 ops 跑 scripts/setup-trial-stripe.sh 拿 priceId 回填 Nacos 后开 rollout。