feat: add synopsis generation endpoint and frontend integration

qwen3-tts-backend/schemas/audiobook.py

@@ -9,6 +9,16 @@ class AudiobookProjectCreate(BaseModel):
     source_text: Optional[str] = None
 
 
+class SynopsisGenerationRequest(BaseModel):
+    genre: str
+    subgenre: str = ""
+    protagonist_type: str = ""
+    tone: str = ""
+    conflict_scale: str = ""
+    num_characters: int = 5
+    num_chapters: int = 8
+
+
 class ScriptGenerationRequest(BaseModel):
     title: str
     genre: str