feat: knowledge-base memory, Dockerfile, docker-compose, CI/release workflows, PR template

Dockerfile

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+FROM python:3.12-slim
+
+WORKDIR /app
+
+# Install dependencies (separate layer for cache efficiency)
+COPY pyproject.toml README.md ./
+COPY steward/ steward/
+RUN pip install --no-cache-dir .
+
+# Create a non-root user (UID/GID 1000) and persistent data directory
+RUN addgroup --gid 1000 steward \
+    && adduser --uid 1000 --gid 1000 --no-create-home --disabled-password --gecos "" steward \
+    && mkdir /data \
+    && chown steward:steward /data
+
+USER steward
+
+# Default path for the thread memory store — override via env or docker-compose
+ENV THREAD_MEMORY_PATH=/data/thread_memory.json
+
+VOLUME ["/data"]
+
+CMD ["steward"]