feat(pipeline): include 'Open, but proposed to close' schools in dims

These schools are still operating and publish results; they drop out
automatically when GIAS flips them to Closed since marts fully rebuild
each run.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pipeline/transform/models/marts/dim_school.sql

@@ -91,4 +91,7 @@ from schools s
 {% if ofsted_relation is not none %}
 left join {{ ref('int_ofsted_latest') }} o on s.urn = o.urn
 {% endif %}
-where s.status = 'Open'
+-- "Open, but proposed to close" schools are still operating (pupils enrolled,
+-- results published) — include them; they drop out automatically once GIAS
+-- flips them to "Closed" (marts are fully rebuilt each run).
+where s.status in ('Open', 'Open, but proposed to close')