Skip RTP padding packets instead of concealing them

Padding/probe packets use a sequence number but carry no audio. They were
treated as lost, so each one played an invented 20 ms frame (a glitch) and
pushed the buffer a frame deeper for drift correction to remove again.
Signature in the first live test: lost ~= drift-drops (74 vs 72 per minute).
They are now skipped and counted as 'padding'.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -40,7 +40,12 @@ Why v2: v1 skipped ahead on an underrun and kept playing from an empty buffer, s
 first hiccup every later wobble was another glitch. It also never corrected for a slow guest
 clock. In simulation that was ~12 glitches/min with a guest clock 30 ppm slow, against ~0
 for v2. The 3 Nov 2026 cohost "jitter" was probably this, but that night was not measured.
-The simulation is kept in `test/jb_sim_test.go.txt` (rename to `_test.go` in the package dir to run).
+The simulation (and a padding regression test, `test/pad_test.go.txt`) is kept in `test/jb_sim_test.go.txt` (rename to `_test.go` in the package dir to run).
+
+Padding fix (v2b, same day): browsers send RTP padding/probe packets that use a sequence
+number but carry no audio. v1/v2 treated each one as a lost packet and played an invented
+frame. That was an audible glitch, plus a frame the drift correction later had to remove
+(signature in the logs: lost ~= drift-drops). They are now skipped and counted as `padding`.
 
 The guest websocket is pinged every 25 s. Without that, the proxy closed it every 90 s
 (signalling only, audio unaffected, but the guest saw "reconnecting...").