feat(discord): add configurable presence (activity/status/type)

- Adds `activity`, `status`, `activityType`, and `activityUrl` to Discord provider config schema.
- Implements a `ReadyListener` in `DiscordProvider` to apply these settings on connection.
- Solves the issue where `@buape/carbon` ignores initial presence options in constructor.
- Validated manually and via existing test suite.

src/config/zod-schema.providers-core.ts

@@ -332,6 +332,10 @@ export const DiscordAccountSchema = z
       .strict()
       .optional(),
     responsePrefix: z.string().optional(),
+    activity: z.string().optional(),
+    status: z.enum(["online", "dnd", "idle", "invisible", "offline"]).optional(),
+    activityType: z.number().int().min(0).max(5).optional(),
+    activityUrl: z.string().optional(),
   })
   .strict();