feat(settings): add per-user Requests visibility toggle

Let users hide request entry points and notifications while existing requests continue running. Keep the setting optional so older clients retain their current behavior.

Ref #1476

packages/types/src/auth.ts

@@ -33,6 +33,7 @@ export const ProvisioningMethod = {
 export type ProvisioningMethod = (typeof ProvisioningMethod)[keyof typeof ProvisioningMethod];
 
 export interface UserSettings {
+  showBookRequests?: boolean;
   syncReaderPreferences?: boolean;
   syncThemePreferences?: boolean;
   statisticsConfig?: import("./statistics").StatisticsSettings;