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/qwen3-tts.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=Qwen3 TTS Backend Service
+After=network.target
+
+[Service]
+Type=simple
+User=bdim
+WorkingDirectory=/opt/qwen3-tts/qwen3-tts-backend
+Environment="PATH=/home/bdim/miniconda3/envs/qwen3-tts-deploy/bin:/usr/local/bin:/usr/bin:/bin"
+ExecStart=/home/bdim/miniconda3/envs/qwen3-tts-deploy/bin/uvicorn main:app --host 0.0.0.0 --port 8884
+Restart=always
+RestartSec=10
+
+[Install]
+WantedBy=multi-user.target