Add mcp matrix entry in docker-publish workflow so the MCP server
image is built and pushed alongside backend/frontend. Also wire the
prebuilt compose file so users can pull and run it directly.
Closes#162
- Build and push backend/frontend images to ghcr.io on every push to main and on version tags
- Add docker-compose.prebuilt.yml for pull-based install (no clone needed)
- Update README Quick Start with inline install one-liner using prebuilt images