chore: update package.json for testing scripts and dependencies

- Added unit and end-to-end testing scripts to package.json.
- Included detox for end-to-end testing and jest-circus for improved test execution.

feat: add testID to LandingScreen logo for better testing

- Added testID attribute to the logo image in LandingScreen for easier identification in tests.

feat: create tokens.ts to re-export design tokens

- Introduced tokens.ts to re-export shared design tokens from lightTheme for consistent imports.

app/e2e/first.e2e.js

@@ -0,0 +1,19 @@
+describe('App basic e2e', () => {
+  beforeAll(async () => {
+    await device.launchApp({ newInstance: true });
+  });
+
+  it('shows the landing splash screen', async () => {
+    // The landing screen shows a logo for 5 seconds before navigating
+    await waitFor(element(by.id('landing-logo')))
+      .toBeVisible()
+      .withTimeout(10000);
+  });
+
+  it('navigates to main tabs after the splash', async () => {
+    // Landing screen auto-navigates after 5s
+    await waitFor(element(by.text('Modèles')))
+      .toBeVisible()
+      .withTimeout(10000);
+  });
+});