feat(automations): implement model eligibility checks for automation creation

- Added model eligibility checks to ensure automations can only use billable models (premium or BYOK).
- Introduced new API endpoint to report model eligibility status for search spaces.
- Updated frontend components to display eligibility alerts and disable creation options when models are not billable.
- Enhanced automation creation forms to reflect model eligibility, preventing users from submitting invalid configurations.
- Implemented server-side logic to capture and preserve model preferences across automation edits, ensuring consistent behavior during execution.

surfsense_backend/app/automations/api/automation.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 from fastapi import APIRouter, Depends, Query, status
+from pydantic import BaseModel
 
 from app.automations.schemas.api import (
     AutomationCreate,
@@ -16,6 +17,17 @@ from app.automations.services import AutomationService, get_automation_service
 router = APIRouter()
 
 
+class ModelEligibilityViolation(BaseModel):
+    kind: str
+    config_id: int | None
+    reason: str
+
+
+class ModelEligibility(BaseModel):
+    allowed: bool
+    violations: list[ModelEligibilityViolation]
+
+
 @router.post(
     "/automations",
     response_model=AutomationDetail,
@@ -47,6 +59,23 @@ async def list_automations(
     )
 
 
+@router.get("/automations/model-eligibility", response_model=ModelEligibility)
+async def get_automation_model_eligibility(
+    search_space_id: int = Query(...),
+    service: AutomationService = Depends(get_automation_service),
+) -> ModelEligibility:
+    """Report whether a search space's models are billable for automations.
+
+    Used by the frontend to gate creation: automations may only use premium
+    global models or user BYOK models (free models and Auto mode are blocked).
+
+    NOTE: declared before ``/automations/{automation_id}`` so the literal path
+    isn't captured by the int-typed ``{automation_id}`` route.
+    """
+    result = await service.model_eligibility(search_space_id=search_space_id)
+    return ModelEligibility.model_validate(result)
+
+
 @router.get("/automations/{automation_id}", response_model=AutomationDetail)
 async def get_automation(
     automation_id: int,