feat: Square client dev mock for online payments and type additions

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

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

backend/internal/square/square.go

@@ -40,6 +40,10 @@ func (p *ProdClient) CreateCardOnFile(ctx context.Context, userID, cardToken str
 	return nil, errors.New("square payments not yet configured — set SQUARE_ACCESS_TOKEN and SQUARE_LOCATION_ID in .env")
 }
 
+func (p *ProdClient) CreateCardOnFileRaw(ctx context.Context, userID, cardNumber string, expMonth, expYear int, cvc string) (*CardOnFile, error) {
+	return nil, errors.New("square payments not yet configured — set SQUARE_ACCESS_TOKEN and SQUARE_LOCATION_ID in .env")
+}
+
 func (p *ProdClient) GetCardsOnFile(ctx context.Context, userID string) ([]CardOnFile, error) {
 	return nil, errors.New("square payments not yet configured — set SQUARE_ACCESS_TOKEN and SQUARE_LOCATION_ID in .env")
 }