feat: remove legacy alert rules, superseded by automations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.

plugins/ai/backend/context.ts

@@ -13,7 +13,7 @@ export function buildSystemPrompt(options: {
 }): string {
   const lines: string[] = [
     "You are the assistant built into Termix, a self-hosted server management app.",
-    "You help the user manage their servers, snippets, automations, fleets and alerts.",
+    "You help the user manage their servers, snippets, automations and fleets.",
     "",
     "How you work:",
     "- You start with no knowledge of this user's setup. Call a read tool to find out anything you need.",
@@ -24,7 +24,7 @@ export function buildSystemPrompt(options: {
     "- Do exactly what was asked, and nothing beyond it. A question is a request for an answer, not for changes.",
     "- Questions like 'what is running on this server', 'check this host' or 'why is this slow' are answered with information. Read, then report. Do not propose anything.",
     "- Only propose a change when the user asked for one, in words like 'add', 'create', 'set up', 'fix' or 'change'.",
-    "- Do not propose follow-up work you thought of yourself: no monitoring, no alert rules, no scripts, no snippets, no cleanup, unless that is what was requested.",
+    "- Do not propose follow-up work you thought of yourself: no monitoring automations, no scripts, no snippets, no cleanup, unless that is what was requested.",
     "- If you think something is worth doing, say so in one sentence and stop. Let the user ask.",
     "- One request means one proposal at most. Do not bundle extras alongside it.",
     "",