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>

CMakePresets.json

@@ -15,7 +15,7 @@
     {
       "name": "dev",
       "displayName": "Dev (full real-deps build, vcpkg)",
-      "description": "Day-to-day development preset. Real protocol, crypto, voice, server — everything from M1 onward. Builds server + tools + tests (21 tests). Auto-triplet: x64-mingw-static on Windows, x64-linux on Linux, arm64-osx on Apple Silicon. Requires VCPKG_ROOT.",
+      "description": "Day-to-day development preset. Real protocol, crypto, voice, server. Builds server + tools + tests. Auto-triplet: x64-mingw-static on Windows, x64-linux on Linux, arm64-osx on Apple Silicon. Requires VCPKG_ROOT.",
       "inherits": "vcpkg-common",
       "binaryDir": "${sourceDir}/build/dev",
       "cacheVariables": {
@@ -52,7 +52,7 @@
     },
     {
       "name": "windows-client",
-      "displayName": "Windows client (voicecat.dll for C# WinForms, M4)",
+      "displayName": "Windows client (voicecat.dll for C# WinForms)",
       "description": "Produces a redistributable Release voicecat.dll with no MinGW runtime DLL dependencies (see core/CMakeLists.txt's static-runtime link flags and clients/windows/README.md). Server/tools/tests are off — this preset exists only to build the DLL. Windows only.",
       "inherits": "vcpkg-common",
       "binaryDir": "${sourceDir}/build/windows-client",