Replace the eager `ensureAudienceVideos()` warm-up (which loaded all three
mood clips per species upfront) with on-demand JIT loading — only the mood
about to be shown is fetched. This saves several megabytes per species since
most conversations never cycle through all moods.
- Remove `ensureAudienceVideos()` and its call in `openAudienceScreen()`
- Load each mood clip only when `show()` is first called for that mood
- Show a letterboxed placeholder for the very first clip until the fetch lands
- Keep whatever is already on screen while a new mood loads in the background
- Add `destroy()` guard to prevent in-flight fetches from mutating a torn-down
container when the audience screen is closed
Also ship the dedicated Kestrelli audience clips (angry, neutral, happy) to
replace the previous human fallback videos for that species.
