fix: hide ????????? after session terminate (0.3.8)

Persist session_terminated in event details, expose in API, and update Events/Dashboard UI.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/tests/test_host_sessions.py

@@ -5,8 +5,10 @@ from types import SimpleNamespace
 from app.services.host_sessions import (
     HostSessionRow,
     _event_login_user,
+    event_session_terminated,
     event_supports_session_terminate,
     filter_logind_session_rows,
+    mark_event_session_terminated,
     parse_loginctl_sessions,
     parse_loginctl_sessions_json,
     parse_qwinsta_sessions,
@@ -130,3 +132,18 @@ def test_terminate_session_for_event_windows_no_actor_user_attr(monkeypatch):
         win_cfg=WinAdminConfig(user="B26\\admin", password="x", source="test"),
     )
     assert result.ok is True
+
+
+def test_event_session_terminated_flag():
+    event = SimpleNamespace(
+        type="rdp.login.success",
+        details={"session_terminated_at": "2026-06-24T10:00:00+00:00"},
+    )
+    assert event_session_terminated(event) is True
+
+    fresh = SimpleNamespace(type="rdp.login.success", details={"user": "alice"})
+    assert event_session_terminated(fresh) is False
+
+    mark_event_session_terminated(fresh, by_username="admin")
+    assert event_session_terminated(fresh) is True
+    assert fresh.details["session_terminated_by"] == "admin"