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/novasonic-server.js

@@ -533,9 +533,6 @@ app.post('/api/youtube/resolve', async (req, res) => {
       execFile(CONFIG.ytdlpBin, [
         '--dump-json', '--flat-playlist', '--no-warnings',
         '--playlist-items', '1-50',
-        // PO token provider (if configured) to get past YouTube's datacenter-IP block. Empty → omitted.
-        ...(CONFIG.potProviderUrl ? ['--extractor-args', `youtubepot-bgutilhttp:base_url=${CONFIG.potProviderUrl}`] : []),
-        ...(CONFIG.ytdlpProxy ? ['--proxy', CONFIG.ytdlpProxy] : []),
         url,
       ], { timeout: 45000, maxBuffer: 20 * 1024 * 1024 }, (err, out, stderr) => {
         if (err && !out?.trim()) return reject(new Error(stderr?.trim() || err.message));