Complete municipal deductions, reductions and benefit fields in DPS #55

Parent epic: #47

Context

Official municipal parameters and DPS layouts cover deductions/reductions and municipal benefits in addition to rates, retention and special regimes. Current support focuses on the most common taxation scenarios.

Goal

Represent the remaining production municipal fiscal groups needed to issue a standards-compliant DPS when a municipality/service requires them.

Scope

• map exact XSD fields for legal deductions/reductions
• map municipal benefit identifiers/values when applicable
• model fields explicitly in DpsData
• validate mutually exclusive/required combinations
• expose no municipality-specific rules beyond official parameters/layout

Constraints

• values must be supplied by the consumer or official parameter data; do not infer entitlement
• preserve backwards-compatible defaults for ordinary service invoices

Tests

• XSD-valid deduction/reduction scenarios
• benefit scenario
• invalid combinations rejected before transport
• ordinary DPS unchanged

Definition of done

• fields documented with official semantic references
• XML validated against supported XSD
• Akaunting can consume them without constructing raw XML