fix: vision(#623): disinto-chat container scaffold (no auth) (#705)

docker/chat/Dockerfile

@@ -0,0 +1,33 @@
+# disinto-chat — minimal HTTP+WebSocket backend for Claude chat UI
+#
+# Small Debian slim base with Python runtime and websockets library.
+# Chosen for simplicity and small image size (~100MB vs ~150MB for Go).
+#
+# Image size: ~100MB (well under the 200MB ceiling)
+#
+# The claude binary is mounted from the host at runtime via docker-compose,
+# not baked into the image — same pattern as the agents container.
+
+FROM debian:bookworm-slim
+
+# Install Python and websockets (no build-time network access needed)
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    python3 \
+    python3-pip \
+    && pip3 install --break-system-packages websockets \
+    && rm -rf /var/lib/apt/lists/*
+
+# Non-root user
+RUN useradd -m -u 1000 -s /bin/bash chat
+
+# Copy application files
+COPY server.py /usr/local/bin/server.py
+COPY entrypoint-chat.sh /entrypoint-chat.sh
+COPY ui/ /var/chat/ui/
+
+RUN chmod +x /entrypoint-chat.sh /usr/local/bin/server.py
+
+USER chat
+WORKDIR /var/chat
+
+ENTRYPOINT ["/entrypoint-chat.sh"]