feat: remove legacy alert rules, superseded by automations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/ui/sidebar/rail-items.ts

@@ -235,13 +235,6 @@ export function visibleRailItems(): RailItemDef[] {
  * title and a mobile entry.
  */
 export const RAIL_UTILITY_ITEMS: RailItemDef[] = [
-  {
-    id: "alerts",
-    icon: Plug,
-    labelKey: "nav.alerts",
-    promotable: true,
-    rightDockable: true,
-  },
   { id: "user-profile", icon: User, labelKey: "nav.userProfile" },
   { id: "admin-settings", icon: Settings, labelKey: "nav.admin" },
 ];