docs(ios): drop stale debug comments + TeamTalk refs from audio router

After the stereo-mic/A2DP debugging settled, the iOS audio code carried
leftover TeamTalk5 comparison notes, source-line citations, TEMP DIAGNOSTIC
markers, and "this was the bug" narratives that no longer help. Reworded
those to state the current rules; kept the comments that document real
constraints (the setPreferredInputNumberOfChannels(2) trap, the re-entrancy
guard, the ma_context no-session-management config).

Comment-only — no behavior change. core builds, ctest --preset dev 21/21.

core/src/audio/audio_engine.h

@@ -301,8 +301,7 @@ class AudioEngine {
     // selected. The iOS Swift layer is the SOLE owner of the audio session (activated in
     // AppState on connect, configured by IOSAudioRouter); miniaudio must only open the
     // AudioUnit against the already-configured, already-active route. These coreaudio fields
-    // are no-ops on non-Apple backends. See PROGRESS.md / the "stereo mic kills output"
-    // investigation.
+    // are no-ops on non-Apple backends.
     static ma_context_config make_context_config();
 
     // Owned context, shared by the playback, capture, and loopback devices so they all honor