feat(otopcua): set Modbus/S7/Galaxy re-discovery policy to Once + Once-branch test (follow-up B)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs

@@ -584,6 +584,15 @@ public sealed class GalaxyDriver
 
     // ===== ITagDiscovery (PR 4.1) =====
 
+    /// <summary>
+    ///     Run-once: <see cref="DiscoverAsync"/> fetches the full Galaxy hierarchy inline and
+    ///     streams the complete node set within a single awaited call — there is no FOCAS-style
+    ///     background cache that fills in after connect. Galaxy is a heavy network driver, so the
+    ///     bounded post-connect retry loop is deliberately avoided; re-discovery on Galaxy
+    ///     redeploy is handled separately via <see cref="IRediscoverable"/> + the deploy-event watcher.
+    /// </summary>
+    public DiscoveryRediscoverPolicy RediscoverPolicy => DiscoveryRediscoverPolicy.Once;
+
     /// <inheritdoc />
     public async Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
     {