feat(ofsted): fall back to ungraded inspection outcome for school grade

Ungraded (Section 8) inspections don't assign a fresh grade — the export
only gives free text like "School remains Good". Parse that text into a
grade (remains Outstanding -> 1, remains Good -> 2, else null) and use it
as a last-resort fallback when no graded overall effectiveness exists.

Also retain schools that have only an ungraded inspection (no graded date)
by coalescing the inspection date, so ~8.5k previously-dropped schools now
carry a grade.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

pipeline/transform/macros/parse_ungraded_outcome.sql

@@ -0,0 +1,20 @@
+-- Macro: Parse an Ofsted ungraded (Section 8) inspection outcome into a grade.
+--
+-- Ungraded inspections do not assign a fresh grade; the outcome is free text
+-- describing whether the school kept its previous judgement, e.g.
+--   "School remains Good", "School remains Good (Concerns) - S5 Next",
+--   "School remains Outstanding", "School remains Outstanding (Concerns) - S5 Next".
+-- These are the only Good/Outstanding signal we can recover, so we match on the
+-- "remains <grade>" phrase (tolerant of any trailing qualifier).
+--
+-- Outcomes that don't establish a Good/Outstanding status — "Standards
+-- maintained", "Improved significantly", "Some aspects not as strong" — map to
+-- null. Grades align with parse_ofsted_grade (1 = Outstanding, 2 = Good).
+
+{% macro parse_ungraded_outcome(column) %}
+    case
+        when {{ column }} ilike '%remains Outstanding%' then 1
+        when {{ column }} ilike '%remains Good%'        then 2
+        else null
+    end
+{% endmacro %}