feat: remove legacy alert rules, superseded by automations

Alert rules already auto-migrate into automations on boot and the old
engine stands down after. Deletes the rule/firing tables, routes, UI,
and AI tools; keeps notification channels since automations still use
them. Also fixes automations' notify step, which still called the
deleted repository.

src/types/homepage-types.ts

@@ -15,7 +15,6 @@ export type WidgetTypeId =
   | "rss_feed"
   | "metrics_chart"
   | "host_grid"
-  | "alert_feed"
   | "ping_status"
   | "recent_activity"
   | "termix_uptime"
@@ -167,11 +166,6 @@ export interface HostGridConfig {
   columns: 2 | 3 | 4;
 }
 
-export interface AlertFeedConfig {
-  maxItems: number;
-  showAcknowledged: boolean;
-}
-
 export interface PingUrl {
   label: string;
   url: string;