feat(FN-2403): add project setup step to onboarding flow

- Introduce a new "project-setup" onboarding step between GitHub and first-task actions
- Gate first-task navigation on project selection and add contextual setup-wizard guidance
- Centralize ordered onboarding step definitions in shared state and reuse them for navigation/progress labels
- Extract ModelOnboardingModal styles into a dedicated component CSS file and update tests/mocks for the new step order

packages/dashboard/app/components/__tests__/QuickChatFAB.test.tsx

@@ -1123,8 +1123,11 @@ describe("QuickChatFAB", () => {
       expect(screen.getByTestId("quick-chat-model-select")).toBeDefined();
     });
 
-    // Open the model dropdown
+    // Open the model dropdown after model loading completes
     const trigger = screen.getByRole("button", { name: "Select model override" });
+    await waitFor(() => {
+      expect(trigger).not.toBeDisabled();
+    });
     fireEvent.click(trigger);
 
     const portalDropdown = await screen.findByTestId("model-combobox-portal");