Catch Geotab billing errors before they become disputes

**Objective:** Audit device billing for month {month} of year {year} (current period by default) and list anything that looks wrong, treating charges of at least {min-value} (default 100) as high.

**Step 1: High charges**

Call `geotab-myadmin-get-device-contract-transaction` with month, year and value-local.min = {min-value}. List each with serial, rate plan, quantity in days and value.

**Step 2: Terminated but billed**

Call `geotab-myadmin-get-device-contract` with terminated = true. Compare its serials with the month's charges from `geotab-myadmin-get-device-contract-transaction` (same month and year). Flag any terminated device charged for a period that starts after its terminated date.

**Step 3: Credits without charges**

Call `geotab-myadmin-get-device-contract-credit-transaction` for the period and flag credited serials that have no charge in the month.

**Step 4: Report**

Three tables (High charges, Terminated but billed, Credits without charges), each with serial and amount, then a one-line count per table. Say which findings most likely need a billing dispute.

**Rules & Guidelines:**

* This is a read-only job. Do NOT call any write tool: no `geotab-myadmin-change-device-billing-plan`, `geotab-myadmin-terminate-device-billing`, `geotab-myadmin-share-device`, `geotab-myadmin-update-device-contracts`, `geotab-myadmin-enroll-device-from-add-in`, `geotab-myadmin-unenroll-device-from-add-in` or any other action tool.
* Flag, do not conclude: a finding is something to check, not a proven error.

**Validation:**

* If a table is empty, say so explicitly.