fix(ai-advice,ui): Bearer auth for proxy gateways + un-pin contact card + VN diacritics

- AI advice handler now sends both `x-api-key` and `Authorization: Bearer`
  so proxy gateways (e.g. chat.trollllm.xyz) accept the request. Native
  Anthropic ignores the extra header.
- Remove `lg:sticky lg:top-20` from listing detail contact card — sidebar
  now scrolls with the page.
- Fix missing Vietnamese diacritics on AI estimate button:
  "Dinh gia AI" -> "Định giá AI", "Dang dinh gia..." -> "Đang định giá...".
  Tests updated accordingly.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/components/valuation/__tests__/ai-estimate-button.spec.tsx

@@ -20,20 +20,20 @@ describe('AiEstimateButton', () => {
 
   it('renders the button', () => {
     render(<AiEstimateButton listingId="listing-1" />);
-    expect(screen.getByText('Dinh gia AI')).toBeInTheDocument();
+    expect(screen.getByText('Định giá AI')).toBeInTheDocument();
   });
 
   it('calls mutate when clicked', async () => {
     const user = userEvent.setup();
     render(<AiEstimateButton listingId="listing-1" />);
 
-    await user.click(screen.getByText('Dinh gia AI'));
+    await user.click(screen.getByText('Định giá AI'));
     expect(mockMutate).toHaveBeenCalledWith('listing-1', expect.any(Object));
   });
 
   it('renders as a button element', () => {
     render(<AiEstimateButton listingId="listing-1" />);
-    expect(screen.getByRole('button', { name: /Dinh gia AI/ })).toBeInTheDocument();
+    expect(screen.getByRole('button', { name: /Định giá AI/ })).toBeInTheDocument();
   });
 });
 
@@ -51,7 +51,7 @@ describe('AiEstimateButton - loading state', () => {
 
     // This test validates the loading button text exists in the component
     render(<AiEstimateButton listingId="listing-1" />);
-    // Component shows 'Dinh gia AI' or 'Dang dinh gia...' based on isPending
+    // Component shows 'Định giá AI' or 'Đang định giá...' based on isPending
     expect(screen.getByRole('button')).toBeInTheDocument();
   });
 });