fix(vat): resolve non-deterministic ORDER BY in TestVAT_ToggleLifecycle

The phase 3 payment query used ORDER BY created_at DESC LIMIT 1.
Within a single transaction, NOW() returns the same timestamp for all
inserts, making the ordering non-deterministic when other parallel tests
insert payment rows with the same timestamp. Fix by parsing the
response's payment ID and querying by it directly.

Also revert eslint.config.js back to error-level rules for all categories
(removing the previous 'warn' overrides).

backend/handlers/payments/vat_test.go

@@ -1202,12 +1202,19 @@ func TestVAT_ToggleLifecycle(t *testing.T) {
 		t.Fatalf("phase 3: expected 200, got %d: %s", w3.Code, w3.Body.String())
 	}
 
+	var phase3Resp CheckoutResponse
+	if err := json.Unmarshal(w3.Body.Bytes(), &phase3Resp); err != nil {
+		t.Fatalf("phase 3: failed to parse response: %v", err)
+	}
+
 	var phase3VAT sql.NullFloat64
 	var phase3Net sql.NullFloat64
 	var phase3VATApplicable bool
 	var phase3Amount float64
-	// Get the latest cash payment (the second one)
-	err = tx.QueryRow(ctx, `SELECT amount, is_vat_applicable, vat_amount, net_amount FROM payments WHERE booking_id = $1 AND payment_method = 'cash' ORDER BY created_at DESC LIMIT 1`, bookingID).Scan(&phase3Amount, &phase3VATApplicable, &phase3VAT, &phase3Net)
+	// Get the specific payment by its ID from the response (avoiding
+	// non-deterministic ORDER BY created_at DESC when NOW() returns the same
+	// transaction start time for all inserts within a transaction).
+	err = tx.QueryRow(ctx, `SELECT amount, is_vat_applicable, vat_amount, net_amount FROM payments WHERE id = $1`, phase3Resp.CheckoutID).Scan(&phase3Amount, &phase3VATApplicable, &phase3VAT, &phase3Net)
 	if err != nil {
 		t.Fatalf("phase 3: failed to query payment: %v", err)
 	}