feat(browse): Wave-0 Batch B — AbCip/TwinCAT/FOCAS opt into online discovery

Task 3/4/5: SupportsOnlineDiscovery => true on AbCipDriver, TwinCATDriver, FocasDriver
(their device enumeration is real, config-gated on EnableControllerBrowse / FixedTree.Enabled
which PatchForBrowse guarantees at open). One gate fact per driver test project.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS/FocasDriver.cs

@@ -427,6 +427,12 @@ public sealed class FocasDriver : IDriver, IReadable, IWritable, ITagDiscovery,
     // node set is non-empty and stable.
     public DiscoveryRediscoverPolicy RediscoverPolicy => DiscoveryRediscoverPolicy.UntilStable;
 
+    /// <summary>The FixedTree device folder is real enumeration — config-gated on FixedTree.Enabled,
+    /// which the universal browser's PatchForBrowse turns on. FOCAS is the UntilStable driver: the
+    /// FixedTree cache fills a couple of seconds post-connect, so the browser's settle loop re-captures
+    /// until the node set is non-empty and stable.</summary>
+    public bool SupportsOnlineDiscovery => true;
+
     /// <inheritdoc />
     public Task DiscoverAsync(IAddressSpaceBuilder builder, CancellationToken cancellationToken)
     {