dashboard: clear deferred items — EventsHub publisher + doc refresh

EventsHub publisher (closes the v2.1 follow-up flagged in the previous commit)

EventStreamService now mirrors every MxEvent it forwards to a gRPC client
into the `EventsHub` group for the session. The fan-out goes through a new
singleton `IDashboardEventBroadcaster`:

  * IDashboardEventBroadcaster — abstraction so EventStreamService doesn't
    take a direct dependency on SignalR.
  * DashboardEventBroadcaster — singleton implementation that hands the
    SendAsync to IHubContext<EventsHub> as fire-and-forget. Errors are
    logged at debug and dropped so the source gRPC stream is never
    blocked.

EventStreamService now takes IDashboardEventBroadcaster as a ctor parameter
and calls Publish(sessionId, publicEvent) once per event after sequence
filtering, before the bounded queue write. Test fixtures and the live
integration harness pass NullDashboardEventBroadcaster.Instance so the
broadcaster is a no-op in unit tests.

SessionDetailsPage adds a "Recent events" panel:
  * implements IAsyncDisposable
  * opens a second HubConnection via DashboardHubConnectionFactory targeting
    /hubs/events
  * calls SubscribeSession(SessionId) on Start
  * renders the most recent 50 events in a small table (worker seq, family,
    server/item handle, alarm reference when the event is OnAlarmTransition)
  * shows a live/offline conn-pill driven by HubConnection.Closed /
    Reconnected events

The dashboard mirror is intentionally passive — events appear only while a
gRPC client is also consuming that session's events. Documented as such in
the empty-state copy and in GatewayDashboardDesign.md.

Documentation refresh

Every doc that referenced the retired options (PathBase, RequireAdminScope,
RequiredGroup) and the old API-key-cookie auth flow is updated to describe
the new model:

  * CLAUDE.md — Authentication section now explains LDAP bind +
    GroupToRole + HubToken bearer flow.
  * gateway.md — Dashboard section: root-mounted routes, snapshot/alarms/
    events SignalR hubs, LDAP cookie + bearer scheme.
  * docs/GatewayConfiguration.md — drop PathBase / RequireAdminScope rows,
    add GroupToRole row, append "Authorization policies" and "SignalR hubs"
    subsections describing the three policies and the /hubs/* endpoints.
  * docs/GatewayDashboardDesign.md — hosting model (root mount, new
    endpoint layout), Realtime Updates rewritten as a hub table
    (DashboardSnapshotHub / AlarmsHub / EventsHub with producers, payloads,
    and routing), Authentication And Authorization rewritten around LDAP +
    role mapping + the hub bearer flow, Configuration block updated.
  * docs/GatewayProcessDesign.md — security-section dashboard paragraph
    and the example config block both refreshed to LDAP/role auth.
  * docs/ImplementationPlanGateway.md — dashboard-auth deliverable list
    updated (LDAP bind + GroupToRole + /hubs/token bearer mint replace the
    API-key login flow).
  * docs/GatewayTesting.md — DashboardLdapLiveTests blurb describes the
    GroupToRole fixture (`{ GwAdmin: Admin }`) instead of the retired
    RequiredGroup default; success-path assertion explains the role-claim
    check.

Verification: 475 server tests, 275 worker tests (+ 9 dev-rig skips), 18
integration tests (live MxAccess + LDAP + Galaxy) all pass — including the
live worker smoke test fixture that now constructs EventStreamService with
the new broadcaster parameter.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.MxGateway.Server/Dashboard/Hubs/DashboardEventBroadcaster.cs

@@ -0,0 +1,41 @@
+using Microsoft.AspNetCore.SignalR;
+using ZB.MOM.WW.MxGateway.Contracts.Proto;
+
+namespace ZB.MOM.WW.MxGateway.Server.Dashboard.Hubs;
+
+/// <summary>
+/// Broadcasts MxEvents to <see cref="EventsHub"/> clients subscribed to the
+/// session's group. Fire-and-forget: we hand the send to the hub context
+/// and return immediately so the source gRPC stream is never blocked.
+/// Errors are logged once and dropped — keeping the SignalR mirror best-effort
+/// preserves the gRPC contract that exists today.
+/// </summary>
+public sealed class DashboardEventBroadcaster(
+    IHubContext<EventsHub> hubContext,
+    ILogger<DashboardEventBroadcaster> logger) : IDashboardEventBroadcaster
+{
+    public void Publish(string sessionId, MxEvent mxEvent)
+    {
+        if (string.IsNullOrEmpty(sessionId) || mxEvent is null)
+        {
+            return;
+        }
+
+        Task send = hubContext.Clients
+            .Group(EventsHub.GroupName(sessionId))
+            .SendAsync(EventsHub.EventMessage, mxEvent);
+
+        if (!send.IsCompletedSuccessfully)
+        {
+            _ = send.ContinueWith(
+                t =>
+                {
+                    if (t.Exception is { } ex)
+                    {
+                        logger.LogDebug(ex, "Dashboard event mirror to session {SessionId} failed.", sessionId);
+                    }
+                },
+                TaskScheduler.Default);
+        }
+    }
+}