[BE-W5-100] Bridge response schema versioning and compatibility tests

[mxllv]

Track
Backend

Difficulty
Medium

Description
Version bridge response schemas to support controlled evolution and safer adapter upgrades.

Acceptance Criteria

• Adapter parses responses via versioned schema handlers.
• Unknown versions fail fast with typed errors and no silent fallback.
• Compatibility tests cover current and previous schema versions.

Tech Stack / Files

• app/services/contracts/sla_adapter.py
• app/services/contracts/translation.py
• tests/test_contract_parity.py

Blocked By
BE-W5-096