Fix MASTER_SETTINGS_KEY type mismatch in PlatformServiceMixin

- Convert MASTER_SETTINGS_KEY from number to string to match method signatures
- Resolves TypeScript errors in PlatformServiceMixin.ts lines 462 & 490
- Maintains backward compatibility with existing database records
- Build verification passed successfully

src/db/tables/settings.ts

@@ -83,6 +83,6 @@ export const SettingsSchema = {
 /**
  * Constants.
  */
-export const MASTER_SETTINGS_KEY = 1;
+export const MASTER_SETTINGS_KEY = "1";
 
 export const DEFAULT_PASSKEY_EXPIRATION_MINUTES = 15;