feat(browse): Wave-0 Batch E — UntilStable settle loop + BrowserSessionService fallback

Task 9: DiscoverTreeAsync UntilStable settle loop (FOCAS) — re-capture on a 1s interval until
        the node set is non-empty and stable across two passes, bounded by open-timeout; on
        timeout with a prior non-empty capture, return it (best-effort) instead of failing.
Task 11: BrowserSessionService resolves bespoke-first, falls back to IUniversalDriverBrowser
         when no bespoke browser matches and CanBrowse is true; new CanBrowse on the service.
16 unit tests green (4 settle + 12 service).

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Browsing/FakeUniversalDriverBrowser.cs

@@ -0,0 +1,20 @@
+using ZB.MOM.WW.OtOpcUa.Commons.Browsing;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Browsing;
+
+/// <summary>Test double for <see cref="IUniversalDriverBrowser"/>. CanBrowse is driven by a
+/// predicate (default: never); OpenAsync delegates to a handler or returns a fresh session.</summary>
+internal sealed class FakeUniversalDriverBrowser : IUniversalDriverBrowser
+{
+    /// <summary>CanBrowse gate. Defaults to "no universal affordance for any type".</summary>
+    public Func<string, string, bool> CanBrowsePredicate { get; init; } = (_, _) => false;
+
+    /// <summary>OpenAsync behavior. Defaults to a fresh FakeBrowseSession.</summary>
+    public Func<string, string, CancellationToken, Task<IBrowseSession>> OpenHandler { get; init; } =
+        (_, _, _) => Task.FromResult<IBrowseSession>(new FakeBrowseSession());
+
+    public bool CanBrowse(string driverType, string configJson) => CanBrowsePredicate(driverType, configJson);
+
+    public Task<IBrowseSession> OpenAsync(string driverType, string configJson, CancellationToken ct) =>
+        OpenHandler(driverType, configJson, ct);
+}