stop fails when the config is invalid, leaving a running stack the tool cannot bring down #25

Description

canton-barebones stop loads and validates the full config before shelling out
to Docker Compose. Any config error (outdated version, unknown key, wrong-typed
field) makes stop exit with the validation error, so the tool cannot bring down
a stack that is already running until the config is fixed. Tearing the stack down
only needs the Compose project name: Docker Compose finds the containers by
project label, no compose files or profiles required.

Steps to reproduce

1. Run canton-barebones start with a valid config
2. Break the config, e.g. set "version": 0 or add an unknown field
3. Run canton-barebones stop

Expected vs actual behavior

Expected: stop reads only composeProjectName and stops the stack. It only
fails, with the usual config error, when that specific field is missing or invalid.

Actual: stop fails with the full config validation error and the stack keeps
running.

Additional context

docker compose --project-name <name> down --remove-orphans works without -f
files, so stop does not need the Splice checkout or the rest of the config.
Other Docker commands (start, reset, status, logs) should keep validating
the full config.