Allow cancelling and deleting pending POS sales

On a sale's detail page, unpaid sales (retail or restaurant) can now be
cancelled or deleted:
- Cancel (pending only) marks it cancelled and frees its table / clears it from
  the kitchen (PosSaleService::cancelSale).
- Delete removes the sale and cascades its lines, modifiers and payments, freeing
  the table first (deleteSale). Paid sales are protected — they can't be deleted.
Status badge now distinguishes cancelled/failed. Covered by PosRestaurantTest.

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

app/Http/Controllers/Pos/SaleController.php

@@ -44,6 +44,32 @@ class SaleController extends Controller
         return view('pos.sales.show', compact('sale', 'invoiceUrl'));
     }
 
+    public function cancel(Request $request, PosSale $sale): RedirectResponse
+    {
+        $this->authorizeOwner($request, $sale);
+
+        try {
+            $this->sales->cancelSale($sale);
+        } catch (RuntimeException $e) {
+            return back()->with('error', $e->getMessage());
+        }
+
+        return redirect()->route('pos.sales.show', $sale)->with('success', 'Sale cancelled.');
+    }
+
+    public function destroy(Request $request, PosSale $sale): RedirectResponse
+    {
+        $this->authorizeOwner($request, $sale);
+
+        try {
+            $this->sales->deleteSale($sale);
+        } catch (RuntimeException $e) {
+            return back()->with('error', $e->getMessage());
+        }
+
+        return redirect()->route('pos.sales.index')->with('success', 'Sale deleted.');
+    }
+
     public function callback(Request $request, PosSale $sale): RedirectResponse
     {
         $reference = trim((string) $request->query('reference', $sale->payment_reference ?? ''));