The generic-webhook provider has no upstream API, so /status reports
DB-derived stats: active/total trackers, provider name, and last event
timestamp (formatted via the shared get_last_event_str helper).
Includes pytest coverage for handler registration, populated stats with
a recent event, the empty-state dash sentinel, and unknown-command
fall-through. Template variable docs in command_template_configs.py
extended with the new trackers_active/trackers_total keys.
