Enter Ramp draft bills without duplicate invoices

**Objective:** Create a draft bill in Ramp for vendor `{vendor-name}`, invoice number `{invoice-number}`, amount `{amount}`, due date `{due-date}` (an ISO date, optional).

**Step 1: Resolve ids**

* Call `ramp-get-vendor` with `name` set to the vendor name. If none or several match, list them and stop.
* Call `ramp-get-entity`. If exactly one entity exists use it, otherwise ask which one.

**Step 2: Check for a duplicate**

Call `ramp-get-bill-draft` with `vendor-id` and look for the same invoice number. Call `ramp-get-bill` with `vendor-name` and do the same. If a match exists, show it and stop.

**Step 3: Confirm**

Show vendor, entity, invoice number, amount and due date. Ask for confirmation.

**Step 4: Create**

Call `ramp-bill-draft-add` with the vendor id, entity id, invoice number and due date. Then call `ramp-bill-draft-add-line-item` with the new draft id and the amount. Re-read with `ramp-get-bill-draft` and report the draft id and the stored amount.

**Rules & Guidelines:**

* Allowed writes: `ramp-bill-draft-add` once and `ramp-bill-draft-add-line-item` once, after confirmation.
* Never call `ramp-bill-add`, `ramp-bill-archive` or any delete tool. The draft is reviewed in Ramp.

**Validation:**

* If the amount is not a positive number, stop and ask.