server: update yt-dlp at server container start

Rather than update yt-dlp at image build,, do this at container run instead to
ensure we always get the latest fixed version.

server/docker-start.sh

@@ -2,6 +2,11 @@
 set -e
 cd /opt/app
 
+mkdir -p /opt/app/bin
+wget -O /opt/app/bin/yt-dlp https://github.com/yt-dlp/yt-dlp/releases/latest/download/yt-dlp
+chmod +x /opt/app/bin/yt-dlp
+export PATH=/opt/app/bin:$PATH
+
 alembic upgrade head
 
 echo "Starting szurubooru API on port ${PORT} - Running on ${THREADS} threads"