feat: use enabled field from config to determine which models run

Changed the API to respect the 'enabled' field in model configurations,
rather than requiring models to be explicitly specified in API requests.

Changes:
- Make 'models' parameter optional in POST /simulate/trigger
- If models not provided, read config and use enabled models
- If models provided, use as explicit override (for testing)
- Raise error if no enabled models found and none specified
- Update response message to show model count

Behavior:
- Default: Only runs models with "enabled": true in config
- Override: Can still specify models in request for manual testing
- Safety: Prevents accidental execution of disabled/expensive models

Example before (required):
  POST /simulate/trigger
  {"config_path": "...", "date_range": [...], "models": ["gpt-4"]}

Example after (optional):
  POST /simulate/trigger
  {"config_path": "...", "date_range": [...]}
  # Uses models where enabled: true

This makes the config file the source of truth for which models
should run, while still allowing ad-hoc overrides for testing.

api/main.py

@@ -31,7 +31,10 @@ class SimulateTriggerRequest(BaseModel):
     """Request body for POST /simulate/trigger."""
     config_path: str = Field(..., description="Path to configuration file")
     date_range: List[str] = Field(..., min_length=1, description="List of trading dates (YYYY-MM-DD)")
-    models: List[str] = Field(..., min_length=1, description="List of model signatures to simulate")
+    models: Optional[List[str]] = Field(
+        None,
+        description="Optional: List of model signatures to simulate. If not provided, uses enabled models from config."
+    )
 
     @field_validator("date_range")
     @classmethod
@@ -107,7 +110,8 @@ def create_app(db_path: str = "data/jobs.db") -> FastAPI:
         """
         Trigger a new simulation job.
 
-        Creates a job with specified config, dates, and models.
+        Creates a job with specified config, dates, and models from config file.
+        If models not specified in request, uses enabled models from config.
         Job runs asynchronously in background thread.
 
         Raises:
@@ -122,6 +126,28 @@ def create_app(db_path: str = "data/jobs.db") -> FastAPI:
                     detail=f"Config path does not exist: {request.config_path}"
                 )
 
+            # Determine which models to run
+            import json
+            with open(request.config_path, 'r') as f:
+                config = json.load(f)
+
+            if request.models is not None:
+                # Use models from request (explicit override)
+                models_to_run = request.models
+            else:
+                # Use enabled models from config
+                models_to_run = [
+                    model["signature"]
+                    for model in config.get("models", [])
+                    if model.get("enabled", False)
+                ]
+
+                if not models_to_run:
+                    raise HTTPException(
+                        status_code=400,
+                        detail="No enabled models found in config. Either enable models in config or specify them in request."
+                    )
+
             job_manager = JobManager(db_path=app.state.db_path)
 
             # Check if can start new job
@@ -135,7 +161,7 @@ def create_app(db_path: str = "data/jobs.db") -> FastAPI:
             job_id = job_manager.create_job(
                 config_path=request.config_path,
                 date_range=request.date_range,
-                models=request.models
+                models=models_to_run
             )
 
             # Start worker in background thread (only if not in test mode)
@@ -152,8 +178,8 @@ def create_app(db_path: str = "data/jobs.db") -> FastAPI:
             return SimulateTriggerResponse(
                 job_id=job_id,
                 status="pending",
-                total_model_days=len(request.date_range) * len(request.models),
-                message=f"Simulation job {job_id} created and started"
+                total_model_days=len(request.date_range) * len(models_to_run),
+                message=f"Simulation job {job_id} created and started with {len(models_to_run)} models"
             )
 
         except HTTPException: