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>

.gitignore

@@ -26,16 +26,16 @@ checkpoints/
 docker/models/
 docker/data/
 docker/.env
-qwen3-tts-frontend/node_modules/
-qwen3-tts-frontend/dist/
-qwen3-tts-frontend/.env
-qwen3-tts-frontend/.env.local
+canto-frontend/node_modules/
+canto-frontend/dist/
+canto-frontend/.env
+canto-frontend/.env.local
 CLAUDE.md
 样本.mp3
 aliyun.md
 /nginx.conf
 deploy.md
-qwen3-tts-backend/scripts
-qwen3-tts-backend/examples
-qwen3-tts-backend/qwen3-tts.service
-qwen3-tts-frontend/.env.production
+canto-backend/scripts
+canto-backend/examples
+canto-backend/canto.service
+canto-frontend/.env.production