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>

core/src/net/transport.h

@@ -3,9 +3,6 @@
  *
  * Design: docs/architecture.md (Net thread), docs/protocol.md §1 (framing).
  * Implementation uses standalone Asio for sockets and timers.
- *
- * Design: docs/architecture.md (Net thread), docs/protocol.md §1 (framing).
- * Implementation uses standalone Asio for sockets and timers.
  */
 #ifndef VOICECAT_NET_TRANSPORT_H
 #define VOICECAT_NET_TRANSPORT_H
@@ -180,7 +177,7 @@ class TcpAcceptor {
     std::vector<std::shared_ptr<TcpServerConn>>      conns_;
 };
 
-// ── UDP media channel (M2) ───────────────────────────────────────────────────
+// ── UDP media channel ────────────────────────────────────────────────────────
 // Thin async UDP socket. send_to() is thread-safe. Recv callbacks fire on the
 // io_context's thread (same thread that runs the io_context::run() loop).
 class UdpMediaChannel {