feat: integrate delete deployment with loading state and fix test modal flow

- Add useDeleteDeployment hook (DELETE /deployments/{id}, refetches list)
- Show spinner + faded row while deletion is in progress; fix race where
  deleteTarget was cleared before isPending resolved by using separate deletingId state
- Redesign StepDeployStatus with animated spinner, ping ring, and success checkmark
- After deploy, "Test" closes the stepper and opens the standalone TestDeploymentModal
  (consistent UI, correct providerId, chat reset on close)
- Prevent closing the stepper modal while deployment is in progress