feat(role): add role_code across schema and APIs

scripts/migrate_add_role_code.sql

@@ -0,0 +1,27 @@
+BEGIN;
+
+ALTER TABLE roles
+  ADD COLUMN IF NOT EXISTS role_code TEXT;
+
+UPDATE roles
+SET role_code = name
+WHERE role_code IS NULL OR btrim(role_code) = '';
+
+ALTER TABLE roles
+  ALTER COLUMN role_code SET NOT NULL;
+
+DO $$
+BEGIN
+  IF NOT EXISTS (
+    SELECT 1
+    FROM pg_constraint
+    WHERE conname = 'uq_roles_system_role_code'
+  ) THEN
+    ALTER TABLE roles
+      ADD CONSTRAINT uq_roles_system_role_code UNIQUE (system_id, role_code);
+  END IF;
+END$$;
+
+CREATE INDEX IF NOT EXISTS idx_roles_role_code ON roles(role_code);
+
+COMMIT;