refactor(localdb): one replication predicate shared by table registration and the alarm drain gate (#603)

The drain gate counted SyncListenPort; a port with no ApiKey shares nothing (fail-closed
passive endpoint), and an ApiKey-only passive node shares its queue but was never gated.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

src/Server/ZB.MOM.WW.OtOpcUa.Runtime/ServiceCollectionExtensions.cs

@@ -177,12 +177,11 @@ public static class ServiceCollectionExtensions
         // possibly deliver its events. Scoping the gate to "is my queue actually shared?" is what
         // keeps the two scopes from disagreeing.
         // BOTH halves of a pair share the queue, but only one of them dials: the initiator sets
-        // Replication:PeerAddress, its partner only sets SyncListenPort and waits. Testing the dial
-        // side alone would leave the listening half permanently ungated — one drainer per pair by
-        // accident rather than by role, and the wrong one whenever the roles swap.
-        var replicated =
-            !string.IsNullOrWhiteSpace(configuration["LocalDb:Replication:PeerAddress"])
-            || !string.IsNullOrWhiteSpace(configuration["LocalDb:SyncListenPort"]);
+        // Replication:PeerAddress, its partner carries the shared ApiKey and waits. The predicate is
+        // LocalDbReplicationPolicy - the same one LocalDbSetup uses to decide which nodes capture
+        // changes at all. It deliberately does NOT count SyncListenPort: the passive endpoint is
+        // fail-closed on the key, so a port with no ApiKey shares nothing and must keep draining.
+        var replicated = LocalDbReplicationPolicy.IsConfigured(configuration);
 
         if (!replicated)
         {