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  * Removed outdated Claude model options from the chat prompt.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/components/hooks/affine/use-ai-chat-config.ts

@@ -1,6 +1,6 @@
 // packages/frontend/core/src/blocksuite/ai/hooks/useChatPanelConfig.ts
-import { AIModelSwitchService } from '@affine/core/modules/ai-button/services/model-switch';
 import { AINetworkSearchService } from '@affine/core/modules/ai-button/services/network-search';
+import { AIPlaygroundService } from '@affine/core/modules/ai-button/services/playground';
 import { AIReasoningService } from '@affine/core/modules/ai-button/services/reasoning';
 import { CollectionService } from '@affine/core/modules/collection';
 import { DocsService } from '@affine/core/modules/doc';
@@ -22,7 +22,7 @@ export function useAIChatConfig() {
 
   const searchService = framework.get(AINetworkSearchService);
   const reasoningService = framework.get(AIReasoningService);
-  const modelSwitchService = framework.get(AIModelSwitchService);
+  const playgroundService = framework.get(AIPlaygroundService);
   const docDisplayMetaService = framework.get(DocDisplayMetaService);
   const workspaceService = framework.get(WorkspaceService);
   const searchMenuService = framework.get(SearchMenuService);
@@ -42,8 +42,8 @@ export function useAIChatConfig() {
     setEnabled: reasoningService.setEnabled,
   };
 
-  const modelSwitchConfig = {
-    visible: modelSwitchService.visible,
+  const playgroundConfig = {
+    visible: playgroundService.visible,
   };
 
   const docDisplayConfig = {
@@ -130,6 +130,6 @@ export function useAIChatConfig() {
     reasoningConfig,
     docDisplayConfig,
     searchMenuConfig,
-    modelSwitchConfig,
+    playgroundConfig,
   };
 }