feat(p7-05): fill signal & log stubs — SignalHandlerTests, ServerLoggerTests

- Add RemovePassFromTrace, RemoveAuthTokenFromTrace, RemoveSecretsFromTrace
  static methods to ServerLogging (mirrors removeSecretsFromTrace/redact in
  server/client.go); uses same regex patterns as Go source to redact only the
  first match's value with [REDACTED].
- Update ClientConnection.RemoveSecretsFromTrace stub to delegate to
  ServerLogging.RemoveSecretsFromTrace.
- Add 2 unit tests to SignalHandlerTests (T:2919 invalid command, T:2920 invalid
  PID); mark 14 process-injection/subprocess tests as deferred ([Fact(Skip=…)]).
- Create ServerLoggerTests with 3 test methods (T:2020, T:2021, T:2022) covering
  NoPasswordsFromConnectTrace, RemovePassFromTrace (8 theory cases),
  RemoveAuthTokenFromTrace (8 theory cases).
- DB: 3 log tests → complete, 2 signal tests → complete, 14 signal tests → deferred.
- All 663 unit tests pass (was 645), 14 deferred skipped.

dotnet/src/ZB.MOM.NatsNet.Server/ClientConnection.cs

@@ -1139,7 +1139,8 @@ public sealed partial class ClientConnection
     internal void ProcessErr(string err)   { /* TODO session 09 */ }
 
     // features 442-443: removeSecretsFromTrace, redact
-    internal static string RemoveSecretsFromTrace(string s) => s;
+    // Delegates to ServerLogging.RemoveSecretsFromTrace (the real implementation lives there).
+    internal static string RemoveSecretsFromTrace(string s) => ServerLogging.RemoveSecretsFromTrace(s);
     internal static string Redact(string s) => s;
 
     // feature 444: computeRTT