fix(twenty-front): keep auto-select model preselection instead of discarding it (#23854)

## Context

Opening the Ask AI panel with a FAST model preselection
(`useOpenAskAiPageWithPreprompt`) sets the chat's model to the
workspace's `fastModel`. For every workspace on default settings that
value is the auto-select sentinel `default-fast-model`.

## Bug

`useAgentChatModelId` validates the selected model against the
enabled-models list — and `useWorkspaceAiModelAvailability` deliberately
filters sentinel ids out of that list. The preselection is therefore
silently discarded (`selectedModelId = null`), the request is sent with
no model, and the server falls back to its default — the **smart**
model. Net effect: FAST preselection no-ops on default-configured
workspaces (observed on twenty-internal: a `model: 'FAST'` entry point
ran on gpt-5.6-sol instead of gpt-5.6-luna).

## Fix

Treat auto-select sentinel ids as always available in the check — the
server-side registry already resolves them (`getEffectiveModelConfig` →
`getDefaultSpeedModel`). One line + a regression test.

## Test

`useAgentChatModelId.test.tsx`: new case asserting a sentinel selection
survives to `modelIdForRequest`; all 4 pass.

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packages/twenty-front/src/modules/ai/hooks/__tests__/useAgentChatModelId.test.tsx

@@ -87,4 +87,13 @@ describe('useAgentChatModelId', () => {
 
     expect(result.current.modelIdForRequest).toBe('openai/gpt-4.1');
   });
+
+  it('should keep an auto-select sentinel selection instead of discarding it', () => {
+    const result = renderHooks({
+      pathname: '/objects/companies',
+      userSelectedModel: 'default-fast-model',
+    });
+
+    expect(result.current.modelIdForRequest).toBe('default-fast-model');
+  });
 });

packages/twenty-front/src/modules/ai/hooks/useAgentChatModelId.ts

@@ -1,4 +1,4 @@
-import { isDefined } from 'twenty-shared/utils';
+import { isAutoSelectModelId, isDefined } from 'twenty-shared/utils';
 
 import { useIsWorkspaceSetupChat } from '@/ai/hooks/useIsWorkspaceSetupChat';
 import { useWorkspaceAiModelAvailability } from '@/ai/hooks/useWorkspaceAiModelAvailability';
@@ -16,6 +16,7 @@ export const useAgentChatModelId = () => {
 
   const isUserModelAvailable =
     !isDefined(agentChatUserSelectedModel) ||
+    isAutoSelectModelId(agentChatUserSelectedModel) ||
     enabledModels.some((model) => model.modelId === agentChatUserSelectedModel);
 
   const selectedModelId = isUserModelAvailable