Add new core functionality and database structures to support WordPress
integration and shipment tracking.
- Add `SyncWordPressUsers` Artisan command to synchronize users between
WordPress and Laravel.
- Create `shipment_items` table migration.
- Fix `discount_codes` enum type by changing `percent` to `percentage`.
- Add `SampleDataSeeder` for testing shipments, transactions, and
discount codes.
- Update project status documentation.
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