fix: add discord to notification provider type

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/config.ts

@@ -21,7 +21,7 @@ export interface BotConfig {
   }
   notifications: {
     enabled: boolean
-    provider: 'bark' | 'ntfy' | 'pushover'
+    provider: 'discord' | 'bark' | 'ntfy' | 'pushover'
     endpoint: string
     alertOnRebalance: boolean
     alertOnError: boolean