feat(phase7.4): order rejection + resubmit flow

- Migration 053: rejection_reason TEXT NULL on orders table
- POST /api/orders/{id}/reject (PM+): sets rejected status, cancels
  active renders, stores reason, notifies creator, broadcasts WS event
- POST /api/orders/{id}/resubmit (creator or PM+): resets to draft,
  clears rejection fields, notifies PMs
- OrderDetail: Reject button (PM+) + inline modal with reason textarea
  and notify-client checkbox; Resubmit button; rejection reason amber
  alert box shown below header when order is rejected
- Orders Kanban: rejection_reason shown as red italic note on card
- Order interface: rejected_at, rejection_reason fields

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/schemas/order.py

@@ -3,9 +3,11 @@ from app.domains.orders.schemas import (
     ComponentData, OrderItemCreate, OrderItemOut,
     OrderLineCreate, OrderLineOut,
     OrderCreate, OrderOut, OrderDetailOut,
+    RejectOrderRequest,
 )
 __all__ = [
     "ComponentData", "OrderItemCreate", "OrderItemOut",
     "OrderLineCreate", "OrderLineOut",
     "OrderCreate", "OrderOut", "OrderDetailOut",
+    "RejectOrderRequest",
 ]