GHSA-3492-cvg7-9mr2: djust: Multi-tenant isolation fails open on the WebSocket/SSE path, disclosing other tenants' data

### Impact `djust.tenants` isolation was enforced only on the HTTP path. The current tenant was stored in `threading.local()` and set exclusively by the HTTP-only `TenantMiddleware`, so on the live (WebSocket/SSE) path `get_current_tenant()` was always `None` during mount and every event handler — and the tenant-aware `QuerySet` manager failed **OPEN** (returned the unfiltered queryset, ignoring `STRICT_MODE`), disclosing **every** tenant's rows to whoever held the socket. `threading.local` was additionally shared across connections on the `sync_to_async` executor thread. …