#7061: Add additional variable to the docker-compose file (default off) to make it work with rootless podman

Volume mounts now accept an `OPENCLAW_VOLUME_OPTS` variable to append mount flags like `:U`, `:Z`, or `:rw`. Defaults to empty (no suffix). This is mainly useful for SELinux-enabled hosts (Fedora, RHEL) where `:Z` is needed for container access to bind mounts or for rootless containers where `:U` is required for UID translation. <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> This PR adds an `OPENCLAW_VOLUME_OPTS` env var that appends a suffix to `docker-compose.yml` bind mounts (e.g. `:U`, `:Z`) so rootless Podman / SELinux hosts can adjust mount labeling/UID shifting without editing the compose file. It also wires the variable through `docker-setup.sh` into `.env` and adds documentation updates plus a new `PODMAN-ROOTLESS.md` guide. <h3>Confidence Score: 4/5</h3> - This PR is low-risk and mostly docs/config changes, with only minor correctness issues in documentation. - The compose interpolation pattern (`${OPENCLAW_VOLUME_OPTS:-}`) is a standard way to add an optional suffix and should be safe for existing Docker users; changes to `docker-setup.sh` are additive and only export/persist the new variable. Main concern is a docs mismatch (Railway guide mentions a compose-only variable) plus a small typo in the new doc file. - docs/railway.mdx (doc correctness), PODMAN-ROOTLESS.md (typo) <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->