feat: configurable traffic threshold and Feishu bot alerts

frontend/src/locales/en-US.json

@@ -778,6 +778,30 @@
     "verifySuccess": "Verification successful",
     "codeError": "Incorrect code. Please try again."
   },
+  "alertSettings": {
+    "title": "Lark alerts",
+    "hint": "The rate threshold detects traffic spikes; per-tunnel quotas remain in tunnel details. Notifications are off by default.",
+    "threshold": "Spike threshold (Mbps)",
+    "webhook": "Feishu / Lark group bot webhook",
+    "secret": "Signing secret (optional)",
+    "optional": "Set if bot signing is enabled",
+    "keepWebhook": "Configured; leave blank to keep",
+    "keepSecret": "Configured; leave blank to keep",
+    "enabled": "Send traffic alerts automatically",
+    "secretHint": "Webhook and signing secret are never shown after saving. The same tunnel event is sent at most once every 5 minutes.",
+    "configure": "Alert settings",
+    "logHint": "Traffic spikes use the platform threshold; quota alerts use each tunnel's traffic policy.",
+    "save": "Save settings",
+    "clear": "Remove bot",
+    "clearConfirm": "This stops notifications and removes bot credentials. In-app alerts remain. Continue?",
+    "cleared": "Bot configuration removed",
+    "saved": "Alert settings saved",
+    "test": "Send test message",
+    "testSent": "Test message sent; check the group",
+    "loadFailed": "Could not load alert settings",
+    "saveFailed": "Could not save alert settings",
+    "testFailed": "Could not send test message"
+  },
   "ipsecPeer": {
     "localParams": "Local IPSec Parameters",
     "loadTemplate": "Load Device Template",