fix(dbt): deduplicate int_ks4_with_lineage predecessor rows

When multiple predecessor URNs exist for the same current school and
year, use DISTINCT ON to keep the one with the most pupils — matching
the same logic already in int_ks2_with_lineage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pipeline/transform/models/intermediate/int_ks4_with_lineage.sql

@@ -16,7 +16,8 @@ with current_ks4 as (
 ),
 
 predecessor_ks4 as (
-    select
+    -- If multiple predecessors have data for the same year, keep the one with most pupils.
+    select distinct on (lin.current_urn, ks4.year)
         lin.current_urn,
         ks4.urn as source_urn,
         ks4.year, ks4.total_pupils, ks4.eligible_pupils, ks4.prior_attainment_avg,
@@ -35,6 +36,7 @@ predecessor_ks4 as (
         where curr.urn = lin.current_urn
           and curr.year = ks4.year
     )
+    order by lin.current_urn, ks4.year, ks4.total_pupils desc nulls last
 ),
 
 combined as (