refactor: rename backend/frontend dirs and remove NovelWriter submodule

- Rename qwen3-tts-backend → canto-backend
- Rename qwen3-tts-frontend → canto-frontend
- Remove NovelWriter embedded repo

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

canto-backend/schemas/voice_design.py

@@ -0,0 +1,28 @@
+from typing import Optional, Dict, Any, List
+from datetime import datetime
+from pydantic import BaseModel, Field
+
+class VoiceDesignCreate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=100)
+    instruct: str = Field(..., min_length=1)
+    meta_data: Optional[Dict[str, Any]] = None
+    preview_text: Optional[str] = None
+
+class VoiceDesignResponse(BaseModel):
+    id: int
+    user_id: int
+    name: str
+    instruct: str
+    meta_data: Optional[Dict[str, Any]]
+    preview_text: Optional[str]
+    ref_audio_path: Optional[str] = None
+    created_at: datetime
+    last_used: datetime
+    use_count: int
+
+    class Config:
+        from_attributes = True
+
+class VoiceDesignListResponse(BaseModel):
+    designs: List[VoiceDesignResponse]
+    total: int