refactor(dockerfile): switch from custom ffmpeg to jellyfin-ffmpeg

- Replace custom ffmpeg image with alpine base and jellyfin-ffmpeg package
- Add symlinks for ffmpeg and ffprobe to standard locations
- Set USER directive to run as nobody for improved security

Containerfile

@@ -1,5 +1,18 @@
-FROM ghcr.io/jrottenberg/ffmpeg:7-alpine
-RUN apk add --no-cache --update bash coreutils gawk grep sed
+FROM alpine:latest
+
+RUN apk add --no-cache --update \
+    bash \
+    coreutils \
+    jellyfin-ffmpeg \
+    gawk \
+    grep \
+    sed
+
+RUN ln -sf /usr/lib/jellyfin-ffmpeg/ffmpeg /usr/local/bin/ffmpeg && \
+    ln -sf /usr/lib/jellyfin-ffmpeg/ffprobe /usr/local/bin/ffprobe
+
 COPY --chown=nobody:nobody --chmod=755 stream-sprout /usr/bin/stream-sprout
+
 EXPOSE 1935
+USER nobody
 ENTRYPOINT [ "stream-sprout" ]