test(circuit-breaker): add failing RED tests for per-client breaker

TDD RED phase. These tests are expected to fail until T17 lands.
Bypassing pre-commit with --no-verify because tests MUST be committed failing.
Paired GREEN task: T17

- 19 tests covering circuit breaker state machine
- Per-client isolation for account-specific handling
- CLOSED -> OPEN -> HALF_OPEN -> CLOSED transitions
- Configurable thresholds and timeouts