Phase 2: exhaustive Subsonic 1.16.1 compatibility matrix, README/config/Docker updates

Dockerfile

@@ -7,7 +7,7 @@ ARG VERSION=dev
 RUN CGO_ENABLED=0 go build -trimpath -ldflags "-s -w -X main.version=${VERSION}" -o /out/vibesonic ./cmd/vibesonic
 
 FROM debian:bookworm-slim
-RUN apt-get update && apt-get install -y --no-install-recommends ffmpeg ca-certificates \
+RUN apt-get update && apt-get install -y --no-install-recommends ffmpeg mpv ca-certificates \
     && rm -rf /var/lib/apt/lists/* \
     && useradd -r -u 10001 -d /data -s /usr/sbin/nologin vibesonic \
     && mkdir -p /data /music \
@@ -25,6 +25,7 @@ ENV VIBESONIC_LISTEN_ADDR=:8080 \
     VIBESONIC_MUSIC_DIRS=/music \
     VIBESONIC_FFMPEG_PATH=/usr/bin/ffmpeg \
     VIBESONIC_FFPROBE_PATH=/usr/bin/ffprobe \
+    VIBESONIC_MPV_PATH=/usr/bin/mpv \
     VIBESONIC_SCAN_INTERVAL=1h
 
 ENTRYPOINT ["/usr/local/bin/vibesonic"]