feat: WooCommerce-first sync + location code filter

Reversed the product sync direction: instead of pulling all 60k+ items
from BC and matching against WooCommerce (600+ paginated API calls that
timeout), now iterates the ~100 WooCommerce products and queries BC for
each one by GTIN/item number (1-2 API calls per product).

Added Location Code setting (e.g. "ICP") to filter stock by BC location.
Uses Item Ledger Entries endpoint to sum per-location stock. Falls back
to total inventory if the endpoint is unavailable.

Also registered wbc_location_code in sync settings group and uninstall.

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

woo-business-central/uninstall.php

@@ -27,6 +27,7 @@ $options_to_delete = array(
     'wbc_default_payment_terms_id',
     'wbc_default_shipment_method_id',
     'wbc_shipping_item_number',
+    'wbc_location_code',
     'wbc_last_sync_time',
     'wbc_encryption_key',
     'wbc_delete_data_on_uninstall',