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>

vcpkg.json

@@ -11,8 +11,8 @@
     { "name": "asio",      "$why": "TCP/UDP/timers reactor — docs/architecture.md" },
     { "name": "sqlite3",   "$why": "server accounts/state — docs/security.md" },
     { "name": "spdlog",    "$why": "logging — docs/tech-stack.md" },
-    { "name": "opus",      "$why": "voice codec (libopus) — docs/voice.md — M2" },
-    { "name": "miniaudio", "$why": "cross-platform capture/playback — docs/tech-stack.md — M2" }
+    { "name": "opus",      "$why": "voice codec (libopus) — docs/voice.md" },
+    { "name": "miniaudio", "$why": "cross-platform capture/playback — docs/tech-stack.md" }
   ],
   "$license-note": "All of the above are permissive (BSD/MIT/ISC/Apache-2.0/public-domain). No GPL/LGPL — see docs/tech-stack.md §5.",
   "$vendored-note": "RNNoise (noise suppression) is NOT a vcpkg dep — its port is !windows !arm — so it is vendored in third_party/rnnoise/ (BSD-3 + CC0). See third_party/README.md and docs/voice.md §10."