chore: expose status port in Docker/compose and document http_addr

EXPOSE 8080 in the image, publish 8080 in compose, document http_addr in the
example config, and add the CPU/memory limits so a long encode can't starve
the host.

Dockerfile

@@ -14,4 +14,5 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 COPY --from=build /videnc-vibe /usr/local/bin/videnc-vibe
 # logs.db + log files land in the working dir — make it the mounted /data so they persist.
 WORKDIR /data
+EXPOSE 8080
 ENTRYPOINT ["videnc-vibe", "-c", "/config/config.yaml"]