Create expense

    Create a new manual expense for the authenticated customer account.
    The expense will be created with the provided details and scheduled for processing.
    
    Required fields include:
    - Type (owner_charge or pmc_expense) - Optional: if not provided, will be automatically calculated from shares array
    - Name and description
    - Expense date
    - Category ID
    - Amount and currency
    - Share configuration for payment and revenue distribution
    
    Type Auto-Calculation:
    - If type is not provided, it will be automatically calculated from the shares array:
      - PMC_EXPENSE: When PMC pays (or both PMC and Owner pay)
      - OWNER_CHARGE: When only Owner pays
    - If type is provided, it must match the calculated type from shares, otherwise validation will fail
    - If shares cannot determine type (no payment shares), type must be provided explicitly