fix(delivery): deliver orders with father-articles and no-payment orders

- Treat an article that has become a father (nIstVater=1) as a free
  position (kArtikel=0) with the name kept: VersandIntern.vBestellPosOffen
  joins tArtikel with nIstVater=0, so such positions could never be
  reserved and failed with "insufficient stock after POS shortage
  booking" (e.g. Becks 42000030).
- Recalculate tAuftragPositionEckdaten before deliverOrder so orders
  without payments get their positions reserved too (previously only
  insertPayment triggered the recalculation).

Also adds debug logging across the delivery pipeline (reserve, commit,
deliver, session, stock-shortage, create-order).

API.md

@@ -79,6 +79,38 @@ Discovers the server and completes pairing with a 6-digit code.
 
 ---
 
+## `GET /v1/newpin` — Generate a pairing code
+
+Creates a fresh, usable 6-digit pairing code on demand. Useful when the static `PAIRING_CODE` has already been consumed by a previous pair.
+
+### Enabling
+
+Disabled by default for security. Enable it by setting `NEWPIN_ENABLED=true` in the environment (`.env`). When disabled, the endpoint returns `403`.
+
+### Response (200)
+
+```json
+{
+  "pin": "482913",
+  "name": "JTL-POS",
+  "serverTimestamp": "2026-08-13 12:00:00"
+}
+```
+
+| Field | Meaning |
+|---|---|
+| `pin` | Fresh 6-digit code; valid until consumed by `GET /v1/client` pairing |
+| `name` | Device name registered on pair (fixed `JTL-POS`) |
+| `serverTimestamp` | Server time at generation |
+
+### Errors
+
+| Status | When |
+|---|---|
+| 403 | `NEWPIN_ENABLED` is not `true` |
+
+---
+
 ## `GET /v1/init` — Sync status
 
 Returns how many entities changed since each cursor. Poll this; only fetch list endpoints when the matching `*_count` is greater than `"0"`.