Split bills + kitchen ingest for online orders

Split bills (restaurant tickets):
- New pos_payments ledger; a tab is settled across one or more cash/Ladill Pay
  payments. The ticket shows total / paid / balance, an amount field with Full /
  ½ / ⅓ / ¼ helpers, and the payments taken. Partial payments keep the tab open;
  the sale finalises (and frees the table) only when the balance hits zero.
  Pay splits get their own checkout + callback (pos.payments.callback).

Pipe online orders to the KDS:
- POST /api/kitchen/orders — a first-party, service-keyed ingest
  (config pos.kitchen_api_keys, scoped by owner, idempotent by external_ref) that
  creates a paid, already-fired ticket (order_type=online, lines source=online).
- The KDS feed is now payment-agnostic (any kitchen-active sale), so paid online
  orders sit on the board next to dine-in tabs and bump the same way; they're
  badged "online".

Schema additive: pos_payments, pos_sales.external_ref. Suite green (14).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/Http/Controllers/Pos/KitchenController.php

@@ -90,8 +90,9 @@ class KitchenController extends Controller
 
     private function buildTickets(string $owner): Collection
     {
+        // Payment-agnostic: dine-in tabs (pending) and paid online orders both
+        // sit on the board while the kitchen is still working them.
         $sales = PosSale::owned($owner)
-            ->openTickets()
             ->where('kitchen_status', PosSale::KITCHEN_ACTIVE)
             ->with(['table', 'lines' => fn ($q) => $q->orderBy('position')->with('modifiers', 'station')])
             ->orderBy('kitchen_sent_at')