feat: remove legacy alert rules, superseded by automations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/locales/en.json

@@ -287,7 +287,6 @@
     "loading": "Loading...",
     "noData": "No data available",
     "allClear": "All clear",
-    "acknowledgeAlert": "Acknowledge",
     "noPingUrls": "No URLs configured",
     "pingLabel": "Label",
     "addPingUrl": "Add URL",
@@ -324,8 +323,6 @@
     "widgetMetricsChartDesc": "Historical CPU, memory, disk or network chart for a host",
     "widgetHostGridName": "Host Grid",
     "widgetHostGridDesc": "Grid view of SSH host statuses",
-    "widgetAlertFeedName": "Alert Feed",
-    "widgetAlertFeedDesc": "Live alert firings with acknowledge support",
     "widgetPingStatusName": "Ping Status",
     "widgetPingStatusDesc": "HTTP ping status for one or more URLs",
     "widgetRecentActivityName": "Recent Activity",
@@ -747,7 +744,6 @@
     "portForwarding": "Forwarding",
     "sftp": "SFTP",
     "connections": "Connections",
-    "alerts": "Alerts",
     "serial": "Serial",
     "keepSideMenuOpen": "Keep Menu Open",
     "collapseSideMenu": "Collapse Menu",
@@ -4950,21 +4946,6 @@
     "viewHistory": "View History"
   },
   "alerts": {
-    "tabFirings": "Alerts",
-    "tabRules": "Rules",
-    "tabChannels": "Channels",
-    "noFirings": "No unacknowledged alerts",
-    "noRules": "No alert rules configured",
-    "noChannels": "No notification channels configured",
-    "rulesDesc": "Alert rules trigger notifications",
-    "channelsDesc": "Where alert notifications are sent",
-    "acknowledge": "Acknowledge",
-    "ackAll": "Ack All",
-    "allAcknowledged": "All alerts acknowledged",
-    "ackFailed": "Failed to acknowledge alert",
-    "ackAllFailed": "Failed to acknowledge all alerts",
-    "showAcknowledged": "Show All",
-    "hideAcknowledged": "Hide Acked",
     "addChannel": "Add Channel",
     "editChannel": "Edit Channel",
     "channelName": "Name",
@@ -4978,21 +4959,10 @@
     "ntfyTopicRequired": "Topic is required",
     "ntfyToken": "Access Token (optional)",
     "channelSaveFailed": "Failed to save channel",
-    "test": "Test",
-    "testSent": "Test notification sent",
-    "testFailed": "Test notification failed",
-    "testFailedWithReason": "Test notification failed: {{reason}}",
-    "addRule": "Add Alert Rule",
-    "editRule": "Edit Alert Rule",
-    "ruleName": "Rule Name",
-    "ruleNameRequired": "Name is required",
-    "triggerType": "Trigger",
-    "thresholdValue": "Threshold (%)",
-    "durationSeconds": "Duration (seconds, 0 = fire immediately)",
-    "cooldownMinutes": "Cooldown (minutes)",
-    "channels": "Notification Channels",
-    "noChannelsHint": "Add channels in the Channels tab first",
-    "ruleSaveFailed": "Failed to save rule"
+    "discordUrlInvalid": "Discord URL must be a valid Discord webhook URL",
+    "discordWebhookDesc": "POST a Discord embed to this webhook URL on each alert firing",
+    "discordUsername": "Display name (optional)",
+    "discordAvatar": "Avatar URL (optional)"
   },
   "ai": {
     "title": "Assistant",