feat(DRW-001) initial commit!

migrations/20260913170640_add_item_grades.up.sql

@@ -0,0 +1,11 @@
+ALTER TABLE items ADD COLUMN min_grade SMALLINT;
+ALTER TABLE items ADD COLUMN max_grade SMALLINT;
+
+-- Backfill any existing shop rows to grade 1-1 (a normal single-grade item)
+-- before the constraint below starts requiring it.
+UPDATE items SET min_grade = 1, max_grade = 1 WHERE source = 'shop';
+
+ALTER TABLE items ADD CONSTRAINT grade_matches_source CHECK (
+    (source = 'shop' AND min_grade >= 1 AND max_grade >= min_grade)
+    OR (source = 'neutral' AND min_grade IS NULL AND max_grade IS NULL)
+);