Alert settings

Every setting below is read from the environment variable in the second column, or from the same key in a YAML configuration file. An unrecognised FANOUT_-prefixed variable is a startup error, so a renamed setting surfaces as a refusal to start rather than as a default nobody chose.

Setting	Environment variable	Type	Default
alerts.enabled	FANOUT_ALERTS_ENABLED	boolean	true
alerts.evaluation_interval	FANOUT_ALERTS_EVALUATION_INTERVAL	duration	30s
alerts.history_days	FANOUT_ALERTS_HISTORY_DAYS	integer	7