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.cpp

@@ -65,7 +65,7 @@ int Server::run() {
     // ── Asio io_context ──────────────────────────────────────────────────────
     asio::io_context io;
 
-    // ── UDP media relay (M2) ─────────────────────────────────────────────────
+    // ── UDP media relay ────────────────────────────────────────────────────────
     auto media_relay = std::make_shared<MediaRelay>(io, registry);
     // Control and media share one port number on TCP+UDP (docs/deployment.md): when media_port
     // is left at 0, follow bind_port so a single forward rule covers both. If bind_port is also 0
@@ -116,7 +116,8 @@ int Server::run() {
             auto tcp = std::make_shared<voicecat::net::TcpServerConn>(
                 std::move(sock), std::move(cbs), std::move(tls));
 
-            // Give session its send/close capability (weak_ptr avoids cycle)
+            // Give session its send/close capability (weak_ptr — see the shared_ptr/cycle
+            // note above).
             std::weak_ptr<voicecat::net::TcpServerConn> weak_tcp = tcp;
             session->set_io(
                 [weak_tcp](std::vector<uint8_t> frame) {