docs(troubleshooting): the audio quality knobs are a request, not a guarantee

The page claimed "audio is a fraction of a percent of a stream's bandwidth, so high costs
nothing worth counting". At 256 kbps plus redundancy that is 512 kbps — true of a 20 Mbps
session, wrong by an order of magnitude on a 5 Mbps one, which is why the budget now exists.
Says what actually happens on a narrow link, and points at the log line that reports the
settled tier.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs-site/content/docs/troubleshooting.md

@@ -339,8 +339,17 @@ PUNKTFUNK_AUDIO_QUALITY=high    # low | standard | high (default high — stereo
 PUNKTFUNK_AUDIO_REDUNDANCY=1    # force the loss-resilient audio plane on (default: automatic)
 ```
 
-Audio is a fraction of a percent of a stream's bandwidth, so `high` costs nothing worth counting.
-`standard` reproduces the pre-0.25 encoder exactly if you want to compare.
+Both are a **request**, not a guarantee: the host budgets audio against the session's video
+bitrate and steps it down on a narrow link, because audio is not managed by adaptive bitrate — so
+whatever it takes is taken off the top. On a roomy link you get 256 kbps plus loss redundancy; as
+the link narrows the host drops redundancy first, then the tier, and never goes below ~96 kbps. The
+session log line says what it settled on:
+
+```
+INFO  punktfunk/1 audio streaming … tier=high kbps=512 redundancy=true
+```
+
+`standard` reproduces the pre-0.25 encoder exactly if you want to A/B it.
 
 ## Audio lags behind the picture