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/plugins/extractors/tap-uk-ofsted/tap_uk_ofsted/tap.py

@@ -59,6 +59,15 @@ COLUMN_PRIORITY = {
         "Latest OEIF sixth form provision",
         "Sixth form provision (where applicable)",
     ],
+    # Ungraded (Section 8) inspection — no fresh grade is assigned; the outcome
+    # is free text like "School remains Good". Used as a last-resort fallback
+    # for the school's grade when no graded overall effectiveness is available.
+    "ungraded_outcome": [
+        "Ungraded inspection overall outcome",
+    ],
+    "ungraded_inspection_date": [
+        "Date of latest ungraded inspection",
+    ],
 }
 
 
@@ -100,6 +109,8 @@ class OfstedInspectionsStream(Stream):
         th.Property("effectiveness_of_leadership_and_management", th.StringType),
         th.Property("early_years_provision", th.StringType),
         th.Property("sixth_form_provision", th.StringType),
+        th.Property("ungraded_outcome", th.StringType),
+        th.Property("ungraded_inspection_date", th.StringType),
         th.Property("report_url", th.StringType),
     ).to_dict()