fix(compare): date report cards with their own inspection date, never the legacy one

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0146VHeLAWjDVE2B5uU67jCB

backend/data_loader.py

@@ -617,6 +617,11 @@ def _ofsted_block(o, urn: int) -> dict:
     block = {
         "framework": o.framework,
         "inspection_date": o.inspection_date.isoformat() if o.inspection_date else None,
+        "rc_inspection_date": (
+            o.rc_inspection_date.isoformat()
+            if getattr(o, "rc_inspection_date", None)
+            else None
+        ),
         "inspection_type": o.inspection_type,
         "overall_effectiveness": overall,
         "grade_source": grade_source,