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/tests/test_compare_enrichment.py

@@ -12,7 +12,8 @@ from fastapi.testclient import TestClient
 LATEST = 202425
 
 CANNED_SUPPLEMENTARY = {
-    "ofsted": {"overall_effectiveness": 2, "grade_source": "graded",
+    "ofsted": {"overall_effectiveness": 2,
+               "current_grade": {"grade": 2, "date": "2023-01-01", "basis": "graded"},
                "report_card": {}, "ofsted_page_url": "https://reports.ofsted.gov.uk/provider/21/100140"},
     "census": {"year": 202526, "fsm_pct": 29.8},
     "admissions": {"year": 202627, "second_preference_offers": 4},
@@ -86,7 +87,7 @@ def test_each_school_gains_supplementary_blocks(client):
     body = client.get("/api/compare?urns=100140,138690").json()
     for urn in ("100140", "138690"):
         school = body["comparison"][urn]
-        assert school["ofsted"]["grade_source"] == "graded"
+        assert school["ofsted"]["current_grade"]["basis"] == "graded"
         assert school["census"]["fsm_pct"] == 29.8
         assert school["admissions"]["second_preference_offers"] == 4
         assert school["admissions_history"][0]["year"] == 202627