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/deploy/qwen-tts.service

@@ -0,0 +1,21 @@
+[Unit]
+Description=Canto Backend API Service
+After=network.target
+
+[Service]
+Type=simple
+User=qwen-tts
+Group=qwen-tts
+WorkingDirectory=/opt/canto-backend
+Environment="PATH=/opt/conda/envs/canto/bin:/usr/local/bin:/usr/bin:/bin"
+EnvironmentFile=/opt/canto-backend/.env
+ExecStart=/opt/conda/envs/canto/bin/python main.py
+Restart=on-failure
+RestartSec=10s
+StandardOutput=append:/var/log/qwen-tts/app.log
+StandardError=append:/var/log/qwen-tts/error.log
+TimeoutStopSec=30s
+KillMode=mixed
+
+[Install]
+WantedBy=multi-user.target