chore: comment cleanup pass ahead of open-sourcing

Removes leftover debug scaffolding (stray Console.WriteLine/NSLog traces,
dead nick_buf_ptr, a no-op --print-config flag now implemented for real),
fixes stale/misleading comments (channel passwords are no longer a "future
M5+" feature, a wrong cross-reference, a stale TlsContext::close() mention,
an incomplete BanRecord::subject_type doc, and a smoke test pointing at a
build/m1-dev preset that no longer exists), strips internal M1-M5 milestone
jargon from comments now that the roadmap is done, trims comments that just
restated the following line, and consolidates a few "why" explanations that
were duplicated 2-3 times in the same file.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

clients/windows/VoiceCat.App/Audio/ProcessAudioMixer.cs

@@ -105,7 +105,6 @@ public sealed class ProcessAudioMixer : IDisposable
                     for (int i = 0; i < frameLen; i++)
                     {
                         int sum = mix[i] + frame[i];
-                        // Saturating clamp
                         mix[i] = (short)Math.Clamp(sum, short.MinValue, short.MaxValue);
                     }
                 }