rm -rf the real /etc/dns dir before symlinking so it replaces rather
than nests. Technitium now writes directly to the persistent
addon_config mount — no entrypoint shim needed.
- root cause: Technitium image ships /etc/dns as a real directory, so the
build-time 'ln -sf /data/dns /etc/dns' created the symlink INSIDE it
(/etc/dns/dns) instead of replacing it. Technitium kept writing to the
ephemeral container directory and lost everything on restart.
- fix: add entrypoint.sh that runs at container start (after HA mounts
volumes), removes the real /etc/dns dir, and symlinks it to /config/dns
(the persistent addon_config mount). Seeds defaults on first run only.
- bump version to 15.4.2
