Improve error message for network report summary

[jdewinne]

Improved error message when network report --summary is run against a non-terminated network:

❯ rdev network ls
ID          NAME                           STATUS          CREATED                           EXPIRES                           POLICY        HAS REPORT
d0254a67    goofy_moore                    assigned        2025-11-03 12:37 PST              -                                 open          no
❯ rdev network report d0254a67 --summary
Error: network report summary not found for network d0254a67, network must be terminated and events must have been porcessed

Usage:
  replicated network report [network-id] [flags]

Example:
  # Get full network traffic report
  replicated network report <network-id>

  # Get aggregated summary with statistics. Only available for networks that have been terminated.
  replicated network report <network-id> --summary

  # Watch for new network events in real-time
  replicated network report <network-id> --watch

Flags:
  -h, --help        help for report
      --id string   Network ID to get report for
      --summary     Get aggregated report summary with statistics instead of individual events
  -w, --watch       Watch for new network events in real-time (polls every 2 seconds)

Global Flags:
      --app string       The app slug or app id to use in all calls
      --debug            Enable debug output
      --profile string   The authentication profile to use for this command
      --token string     The API token to use to access your app in the Vendor API