revert: remove proxy support, restore SpotipyFree-only resolver

IP is not actually blocked (api.spotify.com returns 401, not 403/timeout).
Previous rate limits were temporary. Reverting to the clean state.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -30,7 +30,6 @@ services:
       - MAX_PARALLEL=${MAX_PARALLEL:-2}
       - DOWNLOAD_BACKEND=${DOWNLOAD_BACKEND:-auto}
       - SQUID_QUALITY=${SQUID_QUALITY:-mp3}
-      - SPOTIFY_PROXY=${SPOTIFY_PROXY:-}
     command: >
       sh -c "
         apt-get update && apt-get install -y --no-install-recommends python3 python3-pip ffmpeg curl git && rm -rf /var/lib/apt/lists/* &&