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/Forms/MainForm.cs

@@ -1114,7 +1114,7 @@ public partial class MainForm : Form
             OpenPmWindow(dlg.SelectedUserId);
     }
 
-    // ── M5: Moderation helpers ────────────────────────────────────────────────
+    // ── Moderation helpers ─────────────────────────────────────────────────────
 
     private void UpdateSelfServerMuteState(bool muted, bool deafened)
     {