Returns a map of feature flags enabled for the authenticated user in the context of the current property.
HAS_LEGACY_INVOICES is true when the property holds invoices issued by MFD before it moved to fiscal
documents, whose lines and PDF still live in legacy reporting.
MULTI_INVOICE_PAYMENT_ALLOCATION is false when a payment's receipt may be allocated to one invoice
only; the receipt endpoint then rejects allocations that span several invoices, so payment forms must
not offer them.