refactor: Break apart monolithic configuration schema (#1977)

[skip ci]

src/config/schema/conditions/custom/fullscreen.ts

@@ -0,0 +1,6 @@
+import { z } from 'zod';
+
+export const fullscreenConditionSchema = z.object({
+  condition: z.literal('fullscreen'),
+  fullscreen: z.boolean(),
+});