Add support for RUNNING_APP_STARTING stage and fix import

Fixed two critical issues discovered in deployment logs:

1. **Added RUNNING_APP_STARTING stage support**: HuggingFace introduced
   a new intermediate stage "RUNNING_APP_STARTING" that occurs when the
   container is running but the application inside is still starting up.
   Map this to PENDING status since the health endpoint isn't ready yet.

2. **Fixed DeploymentDefaultEndpoints import**: Corrected import path
   from `zenml.enums` to `zenml.config.deployment_settings` to fix
   ImportError that was preventing health checks from running.

These fixes allow deployments to properly transition through all HuggingFace
Space stages and reach RUNNING status once the app is fully started.

Author: claude

src/zenml/integrations/huggingface/deployers/huggingface_deployer.py

@@ -529,6 +529,7 @@ def do_get_deployment_state(
             elif runtime.stage in [
                 SpaceStage.BUILDING.value,
                 SpaceStage.RUNNING_BUILDING.value,
+                "RUNNING_APP_STARTING",  # New HF stage: app is starting
             ]:
                 status = DeploymentStatus.PENDING
             # Error states - deployment failed or misconfigured
@@ -600,7 +601,9 @@ def _check_deployment_health(
         """
         import requests
 
-        from zenml.enums import DeploymentDefaultEndpoints
+        from zenml.config.deployment_settings import (
+            DeploymentDefaultEndpoints,
+        )
 
         assert deployment.snapshot, "Deployment snapshot not found"