Switch Discord notifications from webhook to user ID DMs

Uses the existing bot token to send DMs to users by their Discord user ID
instead of posting to a channel webhook.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

synculous-client/src/lib/api.ts

@@ -649,7 +649,7 @@ export const api = {
 
     getSettings: async () => {
       return request<{
-        discord_webhook: string;
+        discord_user_id: string;
         discord_enabled: boolean;
         ntfy_topic: string;
         ntfy_enabled: boolean;
@@ -658,7 +658,7 @@ export const api = {
     },
 
     updateSettings: async (data: {
-      discord_webhook?: string;
+      discord_user_id?: string;
       discord_enabled?: boolean;
       ntfy_topic?: string;
       ntfy_enabled?: boolean;