These three roles have multiple variable prefixes each:
- kakaotalk: matrix_appservice_kakaotalk + matrix_appservice_kakaotalk_node
- telegram: matrix_mautrix_telegram + matrix_mautrix_telegram_lottieconverter
- synapse: matrix_synapse + matrix_synapse_customized + matrix_synapse_rust_synapse_compress_state

For each: renamed _docker_image* to _container_image* (and _docker_src*,
_docker_repo* where applicable), added deprecation entries in
validate_config.yml, updated group_vars references, and moved
deprecation tasks to the front of validate_config.yml.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>