chore: update Dockerfile to fix FFmpeg download URL

- Replaced the FFmpeg URL with a version that supports redirection handling using `-L` flag.

backend/Dockerfile

@@ -11,7 +11,7 @@ WORKDIR /tmp/ffmpeg
 RUN apk add --update build-base curl nasm tar bzip2 \
   zlib-dev openssl-dev yasm-dev lame-dev libogg-dev x264-dev libvpx-dev libvorbis-dev x265-dev freetype-dev libass-dev libwebp-dev rtmpdump-dev libtheora-dev opus-dev && \
   DIR=$(mktemp -d) && cd ${DIR} && \
-  curl -s http://ffmpeg.org/releases/ffmpeg-${FFMPEG_VERSION}.tar.gz | tar zxvf - -C . && \
+  curl -L -s https://ffmpeg.org/releases/ffmpeg-${FFMPEG_VERSION}.tar.gz | tar zxvf - -C . && \
   cd ffmpeg-${FFMPEG_VERSION} && \
   ./configure \
   --enable-version3 --enable-gpl --enable-nonfree --enable-small --enable-libmp3lame --enable-libx264 --enable-libx265 --enable-libvpx --enable-libtheora --enable-libvorbis --enable-libopus --enable-libass --enable-libwebp --enable-librtmp --enable-postproc --enable-avresample --enable-libfreetype --enable-openssl --disable-debug && \