feat(shop-sales): ledger contracts + docs for consumer PSP sales tracking

platform/order + platform/event gain the sale.paid and refund.issued wire
contracts (per-rate VatBuckets, PSP provider, timestamps) that drive the
ledger's SHOP-/REFUND- vouchers (go-cart-actor 2b819bd). docs/status.md
records the shop-sales + PSP settlement stack (tickets 17 + 18); the
wayfinder ledger tracker gains the two closed tickets and their Decisions
entries. Bumps go-cart-actor + backoffice (PSP float stat).

🤖 Generated with Codebuff
Co-Authored-By: Codebuff <noreply@codebuff.com>

order/order_test.go

@@ -74,3 +74,48 @@ func TestInvoicePaidRoundTrip(t *testing.T) {
 	}
 }
 
+func TestSalePaidRoundTrip(t *testing.T) {
+	in := SalePaid{
+		OrderID:       "ord-1",
+		PaymentMethod: "stripe",
+		AmountIncVat:  14995,
+		VatBuckets:    []VatBucket{{RateBp: 2500, ExVat: 11996, Vat: 2999}},
+		CapturedAtMs:  1234567890,
+	}
+	raw, err := in.Encode()
+	if err != nil {
+		t.Fatalf("encode: %v", err)
+	}
+	out, err := DecodeSalePaid(raw)
+	if err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if out.OrderID != in.OrderID || out.PaymentMethod != in.PaymentMethod || out.AmountIncVat != in.AmountIncVat || out.CapturedAtMs != in.CapturedAtMs {
+		t.Fatalf("round-trip mismatch: got %+v, want %+v", out, in)
+	}
+	if len(out.VatBuckets) != 1 || out.VatBuckets[0].RateBp != 2500 || out.VatBuckets[0].Vat != 2999 {
+		t.Fatalf("bucket mismatch: %+v", out.VatBuckets)
+	}
+}
+
+func TestRefundIssuedRoundTrip(t *testing.T) {
+	in := RefundIssued{
+		OrderID:      "ord-1",
+		RefundID:     "re_123",
+		AmountIncVat: 7498,
+		VatBuckets:   []VatBucket{{RateBp: 2500, ExVat: 5998, Vat: 1500}},
+		RefundedAtMs: 1234567990,
+	}
+	raw, err := in.Encode()
+	if err != nil {
+		t.Fatalf("encode: %v", err)
+	}
+	out, err := DecodeRefundIssued(raw)
+	if err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	if out.OrderID != in.OrderID || out.RefundID != in.RefundID || out.AmountIncVat != in.AmountIncVat {
+		t.Fatalf("round-trip mismatch: got %+v, want %+v", out, in)
+	}
+}
+