fix: Improve Ollama prompt to always detect Narrator role

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.

backend/services/ollama_service.py

@@ -146,19 +146,26 @@ class OllamaService:
         Returns:
             Formatted prompt string
         """
-        prompt = f"""Analyze the following text and identify all distinct speakers or characters.
+        prompt = f"""Analyze the following text and identify all distinct speakers or characters who need voice assignments.
-Return ONLY a JSON object with a "speakers" array containing the names of speakers.
+
-If there are no clear speakers, return {{"speakers": ["Narrator"]}}.
+CRITICAL: Look for TWO types of content:
+1. NARRATIVE TEXT: Descriptions, scene-setting, "he said", "she thought", etc. → This needs "Narrator"
+2. CHARACTER DIALOGUE: Direct speech by characters → These need character names
+
+You MUST include "Narrator" if there is ANY narrative text, descriptions, or non-dialogue content.
+
+Return ONLY a JSON object with a "speakers" array.
 
 Examples:
-- For dialogue with character names, list those characters
+- Text: "Alice said hello. Bob waved back." → {{"speakers": ["Narrator", "Alice", "Bob"]}}
-- For narrative text, use "Narrator"
+- Text: "Once upon a time, there was a princess." → {{"speakers": ["Narrator"]}}
-- For mixed content, include both characters and "Narrator" if appropriate
+- Text: "The wizard spoke. 'I see danger,' he warned." → {{"speakers": ["Narrator"]}}
+- Text: "Alice: Hello! Bob: Hi there!" → {{"speakers": ["Alice", "Bob"]}}
 
 Text to analyze:
 {text}
 
-Return format: {{"speakers": ["Speaker1", "Speaker2", ...]}}
+Return format: {{"speakers": ["Narrator", "Character1", "Character2", ...]}}
 """
         return prompt