refactor external orders

backend/src/database/migrations/061_add_laufende_nummer.sql

@@ -0,0 +1,14 @@
+-- Add laufende_nummer (sequential number per year) to bestellungen
+ALTER TABLE bestellungen ADD COLUMN laufende_nummer INTEGER;
+
+-- Backfill existing rows with sequential numbers per year
+WITH numbered AS (
+  SELECT id, ROW_NUMBER() OVER (
+    PARTITION BY EXTRACT(YEAR FROM erstellt_am) ORDER BY erstellt_am, id
+  ) AS nr
+  FROM bestellungen
+)
+UPDATE bestellungen b SET laufende_nummer = n.nr FROM numbered n WHERE b.id = n.id;
+
+-- Make NOT NULL after backfill
+ALTER TABLE bestellungen ALTER COLUMN laufende_nummer SET NOT NULL;