Enable bun as yt-dlp JS runtime to avoid throttled stream URLs

Dockerfile

@@ -30,6 +30,13 @@ RUN curl -fsSL \
       -o /usr/local/bin/yt-dlp && \
     chmod +x /usr/local/bin/yt-dlp
 
+# yt-dlp needs a JS runtime to solve YouTube's "n" challenge. Without one the
+# stream URLs it returns are THROTTLED to ~50 KB/s by googlevideo (720p
+# playback stalled / fell back to 144p, saves crawled) and some formats go
+# missing. Only deno is enabled by default; bun is already in this image, so
+# enable it via the system-wide config every yt-dlp invocation reads.
+RUN printf -- '--js-runtimes bun:/usr/local/bin/bun\n' > /etc/yt-dlp.conf
+
 WORKDIR /app
 
 # ---- Install Node/Bun deps ----