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/indextts/s2mel/dac/__init__.py

@@ -0,0 +1,16 @@
+__version__ = "1.0.0"
+
+# preserved here for legacy reasons
+__model_version__ = "latest"
+
+import audiotools
+
+audiotools.ml.BaseModel.INTERN += ["dac.**"]
+audiotools.ml.BaseModel.EXTERN += ["einops"]
+
+
+from . import nn
+from . import model
+from . import utils
+from .model import DAC
+from .model import DACFile