feat: remove legacy alert rules, superseded by automations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/ui-types.ts

@@ -271,7 +271,6 @@ export type KnownTabType =
   | "fleet-inventory"
   // Rail panels that can also open full-width in the main area.
   | "termix-id"
-  | "alerts"
   | "session-logs"
   | "snippets"
   | "macros"