feat(simple_metrics): thread thresholds config from model_config to activity

Reads optional simple_metrics_thresholds from model_config and passes
to calculate_simple_metrics. Threshold schema: {rmse_max, r2_min, ...}.
None when not configured (no alerting, no crash).

Updates workflow tests to expect the new key in the activity-call dict.

SIENTIAPDE-1986

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

tests/laborious/workflows/test_simple_metrics.py

@@ -104,6 +104,7 @@ async def test_run(workflow_mock: AsyncMock, simple_metrics: SimpleMetrics):
             'metrics': input_data['metrics'],
             'interval_minutes': input_data['interval_minutes'],
             'model_type': None,
+            'thresholds': None,
         },
         retry_policy=ANY,
         start_to_close_timeout=ANY,
@@ -211,6 +212,7 @@ async def test_run_default_metrics(workflow_mock: AsyncMock, simple_metrics: Sim
             'metrics': ['rmse', 'mse', 'mae', 'r2'],  # Default value
             'interval_minutes': input_data['interval_minutes'],
             'model_type': None,
+            'thresholds': None,
         },
         retry_policy=ANY,
         start_to_close_timeout=ANY,