feat: rebuild as multi-user web agent

docker/gateway.Dockerfile

@@ -0,0 +1,24 @@
+FROM python:3.12-slim-bookworm@sha256:d50fb7611f86d04a3b0471b46d7557818d88983fc3136726336b2a4c657aa30b
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+WORKDIR /app
+
+RUN apt-get update \
+    && apt-get install --yes --no-install-recommends openssh-client \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY pyproject.toml README.md ./
+COPY agent_platform ./agent_platform
+RUN --mount=type=cache,target=/root/.cache/pip \
+    python -m pip install --upgrade pip==26.1.2 \
+    && python -m pip install .
+
+EXPOSE 8001
+HEALTHCHECK --interval=15s --timeout=5s --retries=10 CMD \
+  python -c "import urllib.request; urllib.request.urlopen('http://127.0.0.1:8001/health', timeout=3)"
+
+# Access to the Docker API is the gateway's purpose. It is never shared with
+# Open WebUI, the model runtime, or user workspace containers.
+CMD ["uvicorn", "agent_platform.gateway.app:app", "--host", "0.0.0.0", "--port", "8001"]