Disable unavailable subreddits after Reddit 404

packages/api-contracts/src/config.ts

@@ -27,6 +27,7 @@ export const RuntimeConfigSchema = z.strictObject({
 });
 export const SubredditConfigSchema = z.strictObject({
   name: z.string(),
+  enabled: z.boolean().default(true),
   type: z.union([z.literal('image'), z.literal('chat')]),
   weight: z.number().optional(),
   tone: ToneKeySchema,