docs: plan names the session's trailer; spec reads the latest visit from dates

The plan hard-coded one model's Co-Authored-By trailer; an executor should use the one its own session specifies. The spec's report-card rule now matches int_ofsted_latest. Review on #183.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/superpowers/specs/2026-10-05-ofsted-current-status-design.md

@@ -81,10 +81,12 @@ Computed once per URN in `int_ofsted_latest`.
 | Latest is ungraded, any other outcome ("Standards maintained", "Improved significantly", "Some aspects not as strong") | the graded inspection's overall grade if it is 1–4, else null | G when a grade is kept | `graded` when a grade is kept |
 | No inspection | null | null | null |
 
-Report cards began in November 2025, after the last legacy graded and ungraded
-inspections, so when a school has a report card it is always the latest visit,
-and no legacy grade stays in force beside it. Ties between G, U and RC on the
-same date resolve in the order report card, graded, ungraded.
+A report card replaced overall grades, so no legacy grade stays in force beside
+one. The latest visit is read from the dates, not assumed: report cards began in
+November 2025, after the last legacy graded and ungraded inspections, and in
+Ofsted's 31 Aug 2026 data no school has a legacy visit newer than its report
+card, but the rule does not depend on that. Ties between G, U and RC on the same
+date resolve in the order report card, graded, ungraded.
 
 Invariants: `current_grade` is null or 1–4; `current_grade_date <=
 latest_visit_date`; `current_grade_basis` is null exactly when `current_grade`