feat: remove legacy alert rules, superseded by automations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.

drizzle/sqlite/meta/_journal.json

@@ -155,6 +155,13 @@
       "when": 1789991403283,
       "tag": "0021_dashing_lester",
       "breakpoints": true
+    },
+    {
+      "idx": 22,
+      "version": "6",
+      "when": 1790083818524,
+      "tag": "0022_steady_the_hood",
+      "breakpoints": true
     }
   ]
 }