fix(pgsql): tie PK sequence to nextval default, setval past data, keep serial defaults

- derive the primary key sequence from the column's nextval() default instead of an unused identity_<table>_<pk> sequence
- setval after table creation (full and diff paths), forward-only, MAX+1 with is_called=false
- do not DROP DEFAULT on serial/bigserial columns without a model default

pkg/writers/pgsql/templates/set_sequence_value.tmpl

@@ -1,6 +1,7 @@
 DO $$
 DECLARE
   m_cnt bigint;
+  m_next bigint;
 BEGIN
   IF EXISTS (
     SELECT 1 FROM pg_class c
@@ -12,8 +13,15 @@ BEGIN
     SELECT COALESCE(MAX({{quote_ident .ColumnName}}), 0) + 1
     FROM {{qual_table .SchemaName .TableName}}
     INTO m_cnt;
-    
-    PERFORM setval('{{qual_table_raw .SchemaName .SequenceName}}'::regclass, m_cnt);
+
+    SELECT CASE WHEN is_called THEN last_value + 1 ELSE last_value END
+    FROM {{qual_table .SchemaName .SequenceName}}
+    INTO m_next;
+
+    -- Only move the sequence forward; never rewind one that is already past the data.
+    IF m_cnt > m_next THEN
+      PERFORM setval('{{qual_table_raw .SchemaName .SequenceName}}'::regclass, m_cnt, false);
+    END IF;
   END IF;
 END;
 $$;