Updated the speaker detection prompt to explicitly instruct the AI to:
- Identify narrative text and assign it to 'Narrator'
- Detect character dialogue and list character names
- Include BOTH Narrator and characters when story has mixed content
This ensures stories with narrative descriptions get proper voice
assignments for both the narrator and speaking characters.
Example: Story with 'Once upon a time...' narrative and dialogue from
Lily, Benny, Sammy now correctly detects all 4 roles.