fix(backend): serve the current Ofsted status from fact_ofsted_latest

The list query and the batch Ofsted fetch each picked 'the latest row' of fact_ofsted_inspection themselves, and _ofsted_block carried an older ungraded grade forward when the latest graded inspection gave none. All three now read marts.fact_ofsted_latest. List rows: ofsted_grade is the grade still in force, ofsted_grade_date when it was awarded or confirmed, ofsted_date the latest visit. The ofsted block gains current_grade and latest_visit and loses grade_source; overall_effectiveness is the graded inspection's own result. A school with only an inspection stays publishable in the sitemap.

Requires fact_ofsted_latest (PR #183's pipeline run) on the database.

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

backend/app.py

@@ -97,8 +97,9 @@ STATIC_SITEMAP_PATHS = ("/", "/rankings", "/compare", "/admissions")
 
 # A page has something a search result could state if any of these is present
 # in any year. Shared by _has_publishable_data and the per-school check in
-# _school_sitemap_rows so the two can never drift.
-_PUBLISHABLE_FIELDS = ("rwm_expected_pct", "attainment_8_score", "ofsted_grade")
+# _school_sitemap_rows so the two can never drift. An inspection with no
+# overall grade (ofsted_date alone) still gives a page something to state.
+_PUBLISHABLE_FIELDS = ("rwm_expected_pct", "attainment_8_score", "ofsted_grade", "ofsted_date")
 
 
 def _has_publishable_data(row) -> bool: