feat(backend): update Square integration, validators, and image validation

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/internal/square/square_dev.go

@@ -14,13 +14,21 @@ import (
 
 var Client SquareClient
 
+var isTesting = os.Getenv("GO_TESTING") == "1"
+
+func mockSleep(d time.Duration) {
+	if !isTesting {
+		time.Sleep(d)
+	}
+}
+
 type MockClient struct {
-	mu          sync.RWMutex
-	cards       map[string]map[string]*CardOnFile
-	checkouts   map[string]*CheckoutResult
-	payments    map[string]*PaymentResult
-	refunds     map[string]*RefundResult
-	completed   map[string]*PaymentResult
+	mu        sync.RWMutex
+	cards     map[string]map[string]*CardOnFile
+	checkouts map[string]*CheckoutResult
+	payments  map[string]*PaymentResult
+	refunds   map[string]*RefundResult
+	completed map[string]*PaymentResult
 }
 
 type devProdClient struct{}
@@ -72,7 +80,7 @@ func NewDevClient() SquareClient {
 
 func (m *MockClient) CreatePayment(ctx context.Context, req CreatePaymentReq) (*PaymentResult, error) {
 	log.Printf("[SQUARE-MOCK] CreatePayment: amount=%d, reference=%s", req.Amount, req.ReferenceID)
-	time.Sleep(1 * time.Second)
+	mockSleep(1 * time.Second)
 
 	m.mu.Lock()
 	defer m.mu.Unlock()
@@ -110,7 +118,7 @@ func (m *MockClient) CreateCheckout(ctx context.Context, req CreateCheckoutReq)
 	m.mu.Unlock()
 
 	go func() {
-		time.Sleep(3 * time.Second)
+		mockSleep(3 * time.Second)
 
 		m.mu.Lock()
 		defer m.mu.Unlock()
@@ -122,7 +130,7 @@ func (m *MockClient) CreateCheckout(ctx context.Context, req CreateCheckoutReq)
 			tipAmount = 500
 			amount += tipAmount
 		}
-		fees := amount*175/10000 // in-person rate: 1.75%
+		fees := amount * 175 / 10000 // in-person rate: 1.75%
 
 		paymentResult := &PaymentResult{
 			ID:          paymentID,
@@ -171,7 +179,7 @@ func (m *MockClient) GetCheckout(ctx context.Context, checkoutID string) (*Payme
 
 func (m *MockClient) RefundPayment(ctx context.Context, req RefundPaymentReq) (*RefundResult, error) {
 	log.Printf("[SQUARE-MOCK] RefundPayment: payment=%s, amount=%d", req.PaymentID, req.Amount)
-	time.Sleep(1 * time.Second)
+	mockSleep(1 * time.Second)
 
 	m.mu.Lock()
 	defer m.mu.Unlock()
@@ -285,4 +293,4 @@ func (m *MockClient) DeleteCardOnFile(ctx context.Context, cardID string) error
 		}
 	}
 	return fmt.Errorf("card not found: %s", cardID)
-}
+}