Replace resemble-perth with a no-op stub

resemble-perth uses uv-build which is incompatible with the old system
pip in the ROCm base image. Since watermarking is unnecessary for
self-hosted private use, stub out the perth module so chatterbox's
import is satisfied without any build complexity.

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

Dockerfile.rocm

@@ -17,6 +17,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /app
 
+COPY perth_stub.py .
+
 # Step 1: Install ROCm-compatible PyTorch stack first.
 # This must happen before anything else to prevent pip from pulling CPU wheels.
 COPY requirements-rocm-init.txt .
@@ -26,15 +28,14 @@ RUN pip3 install -r requirements-rocm-init.txt
 COPY requirements-rocm.txt .
 RUN pip3 install -r requirements-rocm.txt
 
-# Step 3: Install resemble-perth with --no-build-isolation so pip uses the
-# already-installed uv binary instead of an isolated env where it can't find it.
-RUN pip3 install uv && \
-    pip3 install --no-build-isolation \
-        "resemble-perth @ git+https://github.com/resemble-ai/Perth.git@master"
-
 # Step 3: Install chatterbox with --no-deps so pip cannot replace ROCm torch.
 RUN pip3 install --no-deps chatterbox-tts
 
+# Stub out resemble-perth (audio watermarking, unnecessary for self-hosted use).
+# Install as 'perth' module to satisfy chatterbox's import.
+RUN python3 -c "import site; print(site.getsitepackages()[0])" | \
+    xargs -I{} cp /app/perth_stub.py {}/perth.py
+
 # Application source
 COPY engine.py config.py wyoming_handler.py wyoming_voices.py main.py ./