List orphan utters and intents

[rodmaia]

In the list stories screen, show all utters and intents that are not used by any stories.

Tasks

• [ ] Show an intent or utter content box for each orphan item, sorted by name
• [ ] Enable navigation from the content box: edit intent or edit utter
• [ ] Show an "Empty state" when there are no orphans

Acceptance criteria

• [ ] All orphan intents and utters are clearly visible
• [ ] Navigation from content boxes points to the correct locations