Track cancelled deployments separately.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/migrations/011_deployment_cancelled_status.sql

@@ -0,0 +1,10 @@
+DO $$
+BEGIN
+  IF EXISTS (
+    SELECT 1
+    FROM pg_type
+    WHERE typname = 'deployments_status_enum'
+  ) THEN
+    ALTER TYPE deployments_status_enum ADD VALUE IF NOT EXISTS 'cancelled';
+  END IF;
+END $$;