fix(failover): 補 OllamaRoutingResult.health_188 optional 欄位（merge conflict 遺漏）

stash pop 時 --theirs 覆蓋掉了 health_188 dataclass 欄位定義，
導致 to_dict() 拋出 AttributeError（health_188 只在方法內引用）。
補上 health_188: HealthReport | None = None，37 failover tests ✅

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/tests/test_ai_router_failover_integration.py

@@ -59,7 +59,6 @@ def _make_failover_result(
         fallback_chain=fb_endpoints,
         routing_reason=f"test: {primary_provider}",
         health_111=_make_health(HealthStatus.OFFLINE),
-        health_188=None,
     )