chore(admin): remove useless config diff (#12545)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Added a GraphQL mutation to validate multiple app configuration updates, returning detailed validation results for each item.
  - Extended the API schema to support validation feedback, enabling client-side checks before applying changes.
  - Introduced a detailed, parameterized error message system for configuration validation errors.
  - Enabled validation of configuration inputs via the admin UI with clear, descriptive error messages.

- **Improvements**
  - Enhanced error reporting with specific, context-rich messages for invalid app configurations.
  - Simplified admin settings UI by removing the confirmation dialog and streamlining save actions.
  - Improved clarity and maintainability of validation logic and error handling components.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/base/error/def.ts

@@ -877,7 +877,14 @@ export const USER_FRIENDLY_ERRORS = {
   // app config
   invalid_app_config: {
     type: 'invalid_input',
-    message: 'Invalid app config.',
+    args: { module: 'string', key: 'string', hint: 'string' },
+    message: ({ module, key, hint }) =>
+      `Invalid app config for module \`${module}\` with key \`${key}\`. ${hint}.`,
+  },
+  invalid_app_config_input: {
+    type: 'invalid_input',
+    args: { message: 'string' },
+    message: ({ message }) => `Invalid app config input: ${message}`,
   },
 
   // indexer errors