Regenerates the deposit settlement statement ("décompte de sortie") PDF for the lease's
deposit refund and returns the resulting document (an upload carrying a signed, time-limited
file_url). The generator is idempotent: it replaces any previously generated statement.

Use this after adding or changing deductions to refresh the PDF. The lease must have a deposit
refund in progress; otherwise a 422 is returned. The document can also be retrieved later via
GET /api/v1/leasing_contracts/{id}/uploads (filter by nature: deposit_settlement_statements).