fix(dashboard): redact mirror tag values when ShowTagValues off; trim value-log doc (SEC-25, SEC-30)

SEC-25 (near-term hardening; full per-session EventsHub ACL stays deferred to
roadmap item 12): DashboardEventBroadcaster now redacts tag values from a deep
CLONE of the event before mirroring to SignalR when Dashboard:ShowTagValues is
false (the default). Clears MxEvent.value (covers OnDataChange/OnWriteComplete/
OperationComplete/OnBufferedDataChange — their bodies are empty discriminators,
values ride in the top-level field incl. buffered arrays) and the alarm body's
current_value/limit_value. Source event never mutated (shared with the gRPC
path + replay ring) - verified by a source-not-mutated test. Makes the formerly
dead ShowTagValues flag live for the mirror. EventsHub TODO(per-session-acl)
kept and tied to roadmap item 12. Tests: DashboardEventBroadcasterTests (3).

SEC-30: trim docs/Diagnostics.md to mark opt-in command-value logging as NOT
YET IMPLEMENTED (no LogCommandValues knob, RedactCommandValue has no call
sites, no values logged); wiring deferred pending secured-bulk redaction
coverage (SEC-13). No option/call sites added.

Server build clean (0 warnings); Dashboard tests 152/152.

Claude-Session: https://claude.ai/code/session_01DMXXvNuPekkkrTEyPNxEkW

docs/GatewayDashboardDesign.md

@@ -167,7 +167,7 @@ bearer). Each hub class is `[Authorize(Policy = HubClientsPolicy)]`.
 |---|---|---|---|---|
 | `DashboardSnapshotHub` | `/hubs/snapshot` | `DashboardSnapshotPublisher` (BackgroundService consuming `IDashboardSnapshotService.WatchSnapshotsAsync`) | `DashboardSnapshot` | Sent to all connected clients on every snapshot tick; new connections receive the current snapshot synchronously in `OnConnectedAsync`. |
 | `AlarmsHub` | `/hubs/alarms` | `AlarmsHubPublisher` (BackgroundService consuming `IGatewayAlarmService.StreamAsync(filter: null)`) | `AlarmFeedMessage` (`active_alarm` / `snapshot_complete` / `transition`) | Connected clients auto-join `__alarms__`; all clients receive every message. Publisher auto-reconnects every 5s on stream faults. |
-| `EventsHub` | `/hubs/events` | `DashboardEventBroadcaster` invoked by each session's internal dashboard-mirror subscriber on its `SessionEventDistributor` (registered when the session becomes Ready) | `MxEvent` | Clients call `SubscribeSession(sessionId)` to join `session:{id}`. The dashboard is a first-class distributor subscriber, so it receives the session's events whether or not a gRPC client is streaming. It sees RAW session events — not the per-gRPC-subscriber `AfterWorkerSequence` filtering that `EventStreamService` applies at its own boundary — because the dashboard is a separate LDAP-authenticated monitoring view meant to show the session's full event activity (per-session dashboard ACL is tracked separately). |
+| `EventsHub` | `/hubs/events` | `DashboardEventBroadcaster` invoked by each session's internal dashboard-mirror subscriber on its `SessionEventDistributor` (registered when the session becomes Ready) | `MxEvent` | Clients call `SubscribeSession(sessionId)` to join `session:{id}`. The dashboard is a first-class distributor subscriber, so it receives the session's events whether or not a gRPC client is streaming. It sees RAW session events — not the per-gRPC-subscriber `AfterWorkerSequence` filtering that `EventStreamService` applies at its own boundary — because the dashboard is a separate LDAP-authenticated monitoring view meant to show the session's full event activity. Tag values are stripped from the mirrored `MxEvent` copy by `DashboardEventBroadcaster` when `Dashboard:ShowTagValues` is false (the default) — event metadata (tag reference, quality, status, timestamps) still renders, but the value fields are blanked, so no value leaks through this seam. The per-session hub ACL that would scope a Viewer to specific sessions is still outstanding (SEC-25 / remediation roadmap item 12); the value redaction is the near-term hardening that closes the value-leak seam independently of that ACL. |
 
 `DashboardPageBase` opens a `DashboardSnapshotHub` connection via the connection
 factory in `OnInitializedAsync`, seeds `Snapshot` synchronously from
@@ -311,8 +311,9 @@ Right-clicking an attribute (or double-clicking it) adds it to the subscription
 panel. The panel shows each subscribed tag's live value, MXAccess data type,
 quality and source timestamp, refreshed every two seconds. The subscription
 panel is the explicit opt-in tag-value surface: it always shows values
-regardless of `Dashboard:ShowTagValues`, which continues to govern only the
-diagnostic session/worker views.
+regardless of `Dashboard:ShowTagValues`, which governs the diagnostic
+session/worker views and the per-session `EventsHub` mirror (values are
+redacted from the mirrored events when the flag is false).
 
 ### Alarms page