[FEAT] Verify and document rootless Podman support for the Floci container socket

[fredpena]

Cloud & Service / Area

Setup (docker-compose.yml, README)

Problem

PR #287 makes the container socket path configurable with FLOCI_CONTAINER_SOCKET, so podman-compose up no longer fails on the missing /var/run/docker.sock. The Podman side was not reproduced end to end, so a few points are still open:

• Whether the floci container, which runs as UID 1001 with group 0, can use the rootless Podman socket (Lambda and Postgres sidecars start).
• Whether the user socket must be enabled first (systemctl --user enable --now podman.socket) and whether SELinux hosts need extra options.
• The docker run example in the README still hardcodes /var/run/docker.sock.

Proposed

Someone with a rootless Podman host runs the stack with the override, invokes a Lambda function, and records what is needed. Then the README Podman section is updated with the verified steps.

Acceptance

• Lambda invoke works on a rootless Podman host using the documented steps
• README Podman section lists every prerequisite that was actually needed
• docker run example mentions the override or links the Podman section