Spot FreshBooks and ShipStation item drift by SKU

**Objective:** Compare the FreshBooks item list with ShipStation products and stock by SKU, for items matching `{name-filter}` (default all items), and report differences.

**Step 1: Read items (FreshBooks server)**

Call `freshbooks-get-item`, using name.contains set to `{name-filter}` when it is not empty. Keep `sku`, `name`, `unit-cost`, `inventory` and `quantity`. Skip items with no sku and count them.

**Step 2: Read products (ShipStation server)**

Call `shipstation-get-product` and keep `sku`, `name`, `price`, `active` and `upc`. For a long item list, call it once per sku instead.

**Step 3: Read stock (ShipStation server)**

Call `shipstation-get-inventory` and keep `sku`, `on-hand`, `allocated` and `available`. Add up on-hand per sku across locations.

**Step 4: Report**

Three lists: SKUs in FreshBooks but not ShipStation, SKUs in ShipStation but not FreshBooks, and matched SKUs where price differs, the name differs, the product is inactive, or the FreshBooks inventory count differs from ShipStation on-hand. Show both values side by side.

**Rules & Guidelines:**

* `freshbooks-get-item` is on the freshbooks server; `shipstation-get-product` and `shipstation-get-inventory` are on the shipstation server.
* Compare SKUs ignoring case and surrounding spaces.
* Read-only. Do not call `freshbooks-update-item` or `freshbooks-add-item`.

**Validation:**

* If a FreshBooks item has no inventory tracking, leave it out of the stock comparison rather than reporting a mismatch.
* If neither side returns records, say so and stop.