Always broadcast from update_device_status/2 so the device index
LiveView refreshes even when status hasn't changed. Add a 15-second
tick timer to keep "Last Checked" timestamps fresh between polls.
Scope alert PubSub topics to organization for defense-in-depth.
Replace individual Repo.insert() with Repo.insert_all() for sensor readings,
interface stats, processor readings, and storage readings in agent channel and
device poller worker. Add partial/composite database indexes for common query
patterns. Dashboard now uses GROUP BY aggregation instead of loading all devices.
DeviceLive.Show only reloads data for the active tab on PubSub events.
DeviceLive.Index debounces status changes and skips quota queries on updates.
Agent polling preloads filtered to monitored sensors/interfaces only.
