v2.66.3

Fixes

• Docker agent: borg cache and config now persist across container restarts and recreates (#373). They previously lived in /root inside the container and were lost on recreate, forcing borg to re-index every file on the next backup. They now live under the already-persisted /etc/bbs-agent volume — pull the updated agent image and it applies automatically, no compose changes needed. The first backup after the image update rebuilds the cache once; incrementals are fast from then on.