feat(F05): Shipment Management — views, DB schema fix, JOIN bug fix (#3)

- Add 3 JSP views: shipment-list, shipment-form, shipment-view
- Fix DatabaseInitializer to create correct `shipment` table schema
  (shipment_id, order_id, carrier, shipping_status, tracking_number, etc.)
- Fix ShipmentDAO: JOIN `orders` → JOIN `"order"` (reserved word in SQLite)
- Fix Shipment model: remove `final` from id/orderId/addressId fields
  so setter calls in ShipmentController actually take effect
- Add "Add Shipment" button on orderList.jsp for PENDING orders
- Add DEVELOPER_GUIDE.md with Mermaid architecture diagrams

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: salieri009