feat: check the server on launch and remember the selected model

The chat showed 'Server offline' until the user opened Settings, and the selected model was forgotten on every restart. useAutoConnect fetches the models once after the persisted settings are restored; activeModelId is now persisted.

__tests__/useAutoConnect.test.ts

@@ -0,0 +1,42 @@
+import { act, renderHook } from '@testing-library/react-native';
+import { useAutoConnect } from '../hooks/useAutoConnect';
+import * as api from '../services/lmStudioApi';
+import { useAppStore } from '../store/useAppStore';
+
+jest.mock('../services/lmStudioApi');
+
+const mockApi = api as jest.Mocked<typeof api>;
+
+beforeEach(() => {
+    jest.resetAllMocks();
+    useAppStore.setState(useAppStore.getInitialState(), true);
+});
+
+describe('useAutoConnect', () => {
+    it('loads the models once on mount and marks the server connected', async () => {
+        mockApi.getModels.mockResolvedValue([{ id: 'm1', object: 'model', owned_by: 'x' }]);
+        renderHook(() => useAutoConnect());
+
+        await act(async () => {});
+        expect(mockApi.getModels).toHaveBeenCalledTimes(1);
+        expect(useAppStore.getState().isConnected).toBe(true);
+        expect(useAppStore.getState().activeModelId).toBe('m1');
+    });
+
+    it('leaves the app offline when the server does not answer', async () => {
+        mockApi.getModels.mockRejectedValue(new Error('down'));
+        renderHook(() => useAutoConnect());
+
+        await act(async () => {});
+        expect(useAppStore.getState().isConnected).toBe(false);
+    });
+
+    it('does not check again on re-render', async () => {
+        mockApi.getModels.mockResolvedValue([]);
+        const { rerender } = renderHook(() => useAutoConnect());
+        await act(async () => {});
+        rerender({});
+        await act(async () => {});
+        expect(mockApi.getModels).toHaveBeenCalledTimes(1);
+    });
+});