refactor: centralize QWEN fitment saving via save_qwen_fitment()

- Added save_qwen_fitment() in inventory_vehicle_compat.py to centralize
  inserting QWEN results into inventory_vehicle_compat
- Simplified inventory_bp.py create_item() and auto_match_item_vehicles()
  to use the centralized function, removing duplicated INSERT logic

pos/services/inventory_vehicle_compat.py

@@ -369,3 +369,37 @@ def batch_add_compatibilities(tenant_conn, inventory_id, mye_ids, source='manual
     tenant_conn.commit()
     cur.close()
     return inserted
+
+
+def save_qwen_fitment(tenant_conn, inventory_id, fitment_result):
+    """Save QWEN fitment results into inventory_vehicle_compat.
+
+    Args:
+        tenant_conn: Connection to tenant DB.
+        inventory_id: The inventory item ID.
+        fitment_result: Dict from get_vehicle_fitment() with 'vehicles' list.
+
+    Returns:
+        int: Number of compatibilities inserted.
+    """
+    vehicles = fitment_result.get('vehicles', [])
+    if not vehicles:
+        return 0
+
+    inserted = 0
+    cur = tenant_conn.cursor()
+    for v in vehicles:
+        mye_id = v.get('mye_id')
+        if not mye_id:
+            continue
+        cur.execute("""
+            INSERT INTO inventory_vehicle_compat
+                (inventory_id, model_year_engine_id, source, confidence, created_at)
+            VALUES (%s, %s, 'qwen_ai', %s, NOW())
+            ON CONFLICT (inventory_id, model_year_engine_id) DO NOTHING
+        """, (inventory_id, mye_id, fitment_result.get('confidence', 0)))
+        if cur.rowcount > 0:
+            inserted += 1
+    tenant_conn.commit()
+    cur.close()
+    return inserted