fix(agent-manager): add missing NotificationsProvider to provider chain (#551)

The notifications merge (PR #437) added KiloNotifications to ChatView and
NotificationsProvider to the sidebar App.tsx but missed the Agent Manager's
AgentManagerApp.tsx. When ChatView renders inside the Agent Manager, the
useNotifications() call throws because there is no provider — silently
crashing the component tree via SolidJS error boundaries and preventing
session tabs from rendering.