feat: create SEPA Payment Order from Expense Claim

[MarcCon]

Create SEPA Payment Orders from Expense Claims.
Follows the same general logic as for Purchase Invoices.

Key differences compared to Purchase Invoice:

• One payment per Expense Claim (with calculation: grand_total - total_amount_reimbursed)
• Recipient is always the Employee, using the Employee’s bank account
• Additional validation: approval_status = "Approved"
• Add custom SEPA status field for tracking changes

Closes #349

[barredterra]

No SEPA Order Status update logic for Expense Claim (No Status field)

@MarcCon what do you think, should we keep this part analogous to Purchase Invoice as well? This way we could avoid the creation of duplicate payment orders and filter expense claims by payment status.