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>

clients/apple/Tests/VoiceCatCoreTests/VoiceCatClientSmokeTests.swift

@@ -64,7 +64,7 @@ private final class ServerHarness {
         }
         self.port = port
 
-        // Provision a known admin account for moderation/admin tests (M5).
+        // Provision a known admin account for moderation/admin tests.
         let adminURL = URL(fileURLWithPath: repoRoot)
             .appendingPathComponent("build/dev/bin/voicecat-admin")
         guard FileManager.default.isExecutableFile(atPath: adminURL.path) else {
@@ -252,12 +252,12 @@ final class VoiceCatClientSmokeTests: XCTestCase {
         XCTAssertTrue(channels.contains { $0.id == 1 && $0.name == "Lobby" },
                       "expected Lobby (channel 1) in \(channels.map { $0.name })")
 
-        // M5: permissions getter round-trip.
+        // Permissions getter round-trip.
         let perms = client.getPermissions()
         XCTAssertFalse(perms.isAdmin)
         XCTAssertFalse(perms.canKick)
 
-        // M5: guest ListAccounts is rejected by the server with a GenericResult — proves the
+        // Guest ListAccounts is rejected by the server with a GenericResult — proves the
         // moderation wrapper path works end-to-end through the Swift interop layer.
         events.removeAll()
         XCTAssertEqual(client.requestAccountList(), .ok)