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>

server/src/server.h

@@ -18,7 +18,7 @@ struct Config {
     std::string server_name  = "VoiceCat Server";
     std::string data_dir     = "voicecat-data";
     uint16_t    bind_port    = 8384;   // 0 = let OS pick (useful for tests)
-    uint16_t    media_port   = 0;      // M2 UDP media; 0 = follow bind_port (or OS-pick if that's 0)
+    uint16_t    media_port   = 0;      // UDP media port; 0 = follow bind_port (or OS-pick if that's 0)
     bool        allow_guests = true;
     // Called with the actual bound TCP port once the acceptor is ready.
     std::function<void(uint16_t)> on_ready;