feat(core): add ai playground feature flag and remove model switch feature flag (#12934)

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

## Summary by CodeRabbit

* **New Features**
* Added support for the "AI Playground" experimental feature, including
new settings and localization entries.

* **Refactor**
* Renamed configuration and service references from "Model Switch" to
"Playground" across the AI chat and playground interfaces.
* Updated feature flag from "enable_ai_model_switch" to
"enable_ai_playground" for consistency.

* **Bug Fixes**
* The "Model" submenu in AI chat preferences is now always visible,
simplifying menu options.

* **Chores**
  * Removed outdated Claude model options from the chat prompt.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/modules/index.ts

@@ -3,8 +3,8 @@ import { type Framework } from '@toeverything/infra';
 
 import {
   configureAIButtonModule,
-  configureAIModelSwitchModule,
   configureAINetworkSearchModule,
+  configureAIPlaygroundModule,
   configureAIReasoningModule,
 } from './ai-button';
 import { configureAppSidebarModule } from './app-sidebar';
@@ -107,7 +107,7 @@ export function configureCommonModules(framework: Framework) {
   configureCommonGlobalStorageImpls(framework);
   configureAINetworkSearchModule(framework);
   configureAIReasoningModule(framework);
-  configureAIModelSwitchModule(framework);
+  configureAIPlaygroundModule(framework);
   configureAIButtonModule(framework);
   configureTemplateDocModule(framework);
   configureBlobManagementModule(framework);