fix(docker): pre-create /home/node/.gemini with correct ownership (#747)

Docker bind-mounts auto-create missing parent directories as root.
When docker-compose mounts files into /home/node/.gemini/, the directory
ends up root-owned, causing gemini CLI to crash with EACCES when writing
projects.json.

Pre-create the directory and chown to node:node before switching to
USER node.

Closes #740

Co-authored-by: 超渡法師 <chaodu@openab.dev>

Author: chaodu-agent

Dockerfile.gemini

@@ -27,6 +27,8 @@ WORKDIR /home/node
 
 COPY --from=builder --chown=node:node /build/target/release/openab /usr/local/bin/openab
 
+RUN mkdir -p /home/node/.gemini && chown -R node:node /home/node/.gemini
+
 USER node
 HEALTHCHECK --interval=30s --timeout=5s --retries=3 \
   CMD pgrep -x openab || exit 1