revert: drop the YouTube cookies/PO-token/proxy workarounds (back to pre-saga state)

None of it got downloads working on the flagged datacenter IP (web_music media
403, then 429 rate-limiting), so revert the whole lot to keep things clean:
- config.js: remove potProviderUrl + ytdlpProxy
- ytdlp.js: remove potArgs/proxyArgs; player_client back to web_music,default
- novasonic-server.js: remove pot/proxy args from importer resolve
- docker-compose.yml: remove the bgutil-provider service + backend env/plugin/depends_on
- CHANGELOG: drop the [2.2] section

Kept the one genuine fix: a failed direct-link download now reports failure
(moved its note into [2.1]).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/lib/config.js

@@ -8,14 +8,6 @@ const CONFIG = {
   maxParallel:     parseInt(process.env.MAX_PARALLEL || '2', 10),
   downloadBackend: (process.env.DOWNLOAD_BACKEND || 'ytdlp').toLowerCase(),
   ticketmasterKey:     process.env.TICKETMASTER_API_KEY  || '',
-  // YouTube 403s media downloads from datacenter IPs without a PO ("Proof of Origin") token, which
-  // yt-dlp can't compute itself. The bgutil-ytdlp-pot-provider plugin fetches tokens from a small
-  // provider service; set its URL here (e.g. http://bgutil-provider:4416). Empty → no PO token used
-  // (yt-dlp runs exactly as before). See docker-compose.yml.
-  potProviderUrl:  process.env.POT_PROVIDER_URL || '',
-  // Optional proxy for yt-dlp (e.g. a residential/rotating proxy) — the durable fix when the
-  // datacenter IP stays flagged (403/429) even with a PO token. Empty → yt-dlp runs directly.
-  ytdlpProxy:      process.env.YTDLP_PROXY || '',
 };
 
 module.exports = CONFIG;