fix: restore onboarding modal bottom padding and stop leftover scrollbars (#16684)

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: hieptl <hieptl.developer@gmail.com>

__tests__/components/onboarding/onboarding-modal.test.tsx

@@ -735,6 +735,12 @@ describe("OnboardingModal", () => {
     const scrollArea = screen.getByTestId("onboarding-scroll-area");
     const rail = screen.getByTestId("onboarding-slide-rail");
     expect(scrollArea.contains(rail)).toBe(true);
+    // Bottom padding matches the header (`pt-7`) so the last control is
+    // not flush against the modal edge. The region must size to its
+    // content (`min-h-0` + overflow, no `flex-1`) so a content-fitting
+    // step does not paint a leftover scrollbar.
+    expect(scrollArea).toHaveClass("pb-7");
+    expect(scrollArea).not.toHaveClass("flex-1");
   });
 
   it("keeps the LLM step heading and Back/Next outside the scrollable settings body", async () => {

src/components/features/onboarding/onboarding-modal.tsx

@@ -314,7 +314,7 @@ export function OnboardingModal({
 
           <div
             data-testid="onboarding-scroll-area"
-            className="flex-1 min-h-0 overflow-y-auto custom-scrollbar-always px-7"
+            className="min-h-0 overflow-y-auto custom-scrollbar-always px-7 pb-7"
           >
             <div
               data-testid="onboarding-slide-rail"