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>

laborious/workflows/simple_metrics.py

@@ -32,6 +32,7 @@ class SimpleMetrics:
         model_config = input_data['model_config']
         target_name = model_config['target']
         model_type = model_config.get('model_type')
+        thresholds = model_config.get('simple_metrics_thresholds')
 
         query = f"""
             select p."timestamp", p.prediction, ld.value as "target"
@@ -72,6 +73,7 @@ class SimpleMetrics:
                 'metrics': input_data.get('metrics', ['rmse', 'mse', 'mae', 'r2']),
                 'interval_minutes': interval_minutes,
                 'model_type': model_type,
+                'thresholds': thresholds,
             },
             retry_policy=retry_policy,
             start_to_close_timeout=timedelta(seconds=300),