fix: correct category-page size and brand/category source of truth

Two fixes bundled together:

1. Shrink CATEGORY_PAGE_SIZE from 100 to 25. Each item in a category page
   can trigger several sequential BC calls (location stock, price lists,
   brand/category lookup) beyond the page fetch itself - at 100 items/page
   this measured 150-250+ seconds on live data, exceeding PHP's execution
   limit and leaving the Action Scheduler action stuck "in-progress"
   forever instead of completing or failing visibly.

2. BC's Item Category table has no parent-category field - confirmed via
   the actual published CategProd endpoint (Code, Description only) and
   the standard itemCategories entity (id, code, displayName only). The
   original ItemCategoryHierarchy AL snippet assumed a Parent Category
   field that doesn't exist. Switched to the standard /itemCategories API
   for the brand display name (no custom endpoint needed for that part),
   and replaced the BC-side parent-category walk with a WordPress-side
   manual map (wbc_category_parent_map: "CODE=Parent Name" per line) for
   the WooCommerce product category grouping, since BC has nothing to
   offer there.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

woo-business-central/includes/class-wbc-batch-sync.php

@@ -29,8 +29,16 @@ class WBC_Batch_Sync {
 
     /**
      * Number of BC items fetched per page in category-filtered mode
+     *
+     * Kept small on purpose: each item can trigger several sequential BC
+     * calls while processing it (location stock, price lists, brand/category
+     * lookup), not just the one page fetch. 100 items/page was measured to
+     * take 150-250+ seconds per page - long enough to exceed PHP's
+     * execution limit and strand the action mid-run ("in-progress" forever,
+     * never completing or erroring). Matches BATCH_SIZE, which is proven to
+     * finish reliably within one execution.
      */
-    const CATEGORY_PAGE_SIZE = 100;
+    const CATEGORY_PAGE_SIZE = 25;
 
     /**
      * Option name storing the current/last run's progress