feat(client): streamEvents() wraps server-streaming audit log

Adds `HubClient.streamEvents(backfill:, types:)` returning a
`Stream<LoggedEvent>` that fronts the new
`HubAdmin/StreamEvents` RPC. Each event arrives the instant
the hub appends it; cancel the subscription to close the RPC.

`backfill` defaults to 50 historical events (oldest-last for
chronological reception). `RESOURCE_EXHAUSTED` from the
server means the receiver fell behind — reconnect with a
fresh backfill to resync.

Bindings regenerated from fai_platform/proto.

dart analyze + dart test green (4 tests).

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/src/hub_client.dart

@@ -158,6 +158,25 @@ class HubClient {
     return r.events;
   }
 
+  /// Server-streaming audit-log subscription. The hub first
+  /// replays up to [backfill] historical events (oldest-last so
+  /// the receiver sees them in chronological order), then keeps
+  /// the stream open and forwards every newly-appended event as
+  /// soon as it lands.
+  ///
+  /// Cancel the returned [Stream]'s subscription to close the
+  /// RPC. If the server reports `RESOURCE_EXHAUSTED` ("stream
+  /// lagged"), reconnect with backfill to resync.
+  Stream<LoggedEvent> streamEvents({
+    int backfill = 50,
+    List<String> types = const [],
+  }) {
+    final req = pb.StreamEventsRequest()
+      ..backfill = backfill
+      ..eventTypes.addAll(types);
+    return _admin.streamEvents(req);
+  }
+
   /// Pending approvals filtered by status. Defaults to all.
   Future<List<PendingApprovalEntry>> listApprovals({
     List<String> statuses = const [],