Restaurant mode Phase 3: table-QR self-ordering into the kitchen

The "links" slice — a guest scans a table's QR, browses the menu (with
modifiers), and submits an order that lands on that table's open tab and fires
straight to the Kitchen Display.

- Public, auth-free flow scoped by an unguessable table short_code:
  GET /t/{code} (menu + client cart), POST /t/{code}/order (throttled),
  GET /t/{code}/done. Orders open/append the table's dine-in tab, add lines as
  source=guest, and send to the kitchen.
- Staff print a per-table QR (Settings → table → QR; renders client-side to the
  public menu URL). short_code is generated lazily.
- Guest lines are badged on the ticket and the KDS so staff can tell them apart;
  staff still settle the tab as usual (cash / Ladill Pay).
- Extracted PosSaleService::buildProductLine as the single product+modifier
  price resolver, now shared by staff and guest ordering (client prices never
  trusted).

Schema additive: pos_tables.short_code, pos_sale_lines.source. New
PosRestaurantTest covers the guest order firing to the kitchen; suite green (12).

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

app/Http/Controllers/Pos/TableController.php

@@ -42,4 +42,14 @@ class TableController extends Controller
             'openTickets' => $openTickets,
         ]);
     }
+
+    public function qr(Request $request, PosTable $table): View
+    {
+        $this->authorizeOwner($request, $table);
+
+        return view('pos.tables.qr', [
+            'table' => $table,
+            'url' => route('pos.table.menu', $table->ensureShortCode()),
+        ]);
+    }
 }