* refactor: Store SSH keys in subdirectory for cleaner volume mounting
Change SSH key location from ~/.ssh/compose-farm (file) to
~/.ssh/compose-farm/id_ed25519 (file in directory).
This allows docker-compose to mount just the compose-farm directory
to /root/.ssh without exposing all host SSH keys to the container.
Also make host path the default option in docker-compose.yml with
clearer comments about the two options.
* docs: Update README for new SSH key directory structure
* docs: Clarify cf ssh setup must run inside container
Config search order is now:
1. --config CLI option
2. CF_CONFIG environment variable
3. ./compose-farm.yaml
4. ~/.config/compose-farm/compose-farm.yaml
Docker workflow simplified: mount compose_dir once, set CF_CONFIG
to config file within it. No more symlink issues or multiple mounts.
