Redesign project header and study navigation

- Header: navigation buttons grouped; Study Guide, Podcast, and
  Pronunciation Guide move into a Tools menu (disabled until a chunk
  exists), set apart from Export and Share by a divider.
- Only one header dropdown is open at a time, and it closes on an
  outside click or Escape.
- Study page: drop the duplicate Prev/Next and counter at the top; the
  fixed bottom bar is the single chunk navigation and now shows a
  readable "Chunk N of M".
- Mobile empty-state hint points to Back to Chunks.
- Tests: Tools menu, one-dropdown-at-a-time, Escape/outside click.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/App.test.jsx

@@ -702,3 +702,35 @@ describe('Chunk builder', () => {
     expect(await screen.findByRole('button', { name: 'Titus 2' })).toHaveClass('bg-slate-900');
   });
 });
+
+// ---------------------------------------------------------------------------
+// Header redesign: Tools menu + one-dropdown-at-a-time
+// ---------------------------------------------------------------------------
+describe('Header menus', () => {
+  test('Tools is disabled until a chunk exists, then opens the Pronunciation Guide', async () => {
+    const user = await loadChapter();
+    expect(screen.getByRole('button', { name: /tools/i })).toBeDisabled();
+    addChunk('Paul, a servant', 'Paul, a servant');
+    await screen.findByText('1 created');
+    await user.click(screen.getByRole('button', { name: /tools/i }));
+    await user.click(screen.getByRole('button', { name: /pronunciation guide/i }));
+    expect(await screen.findByRole('heading', { name: /pronunciation guide/i })).toBeInTheDocument();
+  });
+
+  test('opening one dropdown closes the other; Escape and outside clicks close it', async () => {
+    const user = await loadChapter();
+    await user.click(screen.getByRole('button', { name: /export/i }));
+    expect(screen.getByRole('button', { name: /export markdown/i })).toBeInTheDocument();
+
+    await user.click(screen.getByRole('button', { name: /share/i }));
+    expect(screen.queryByRole('button', { name: /export markdown/i })).not.toBeInTheDocument();
+    expect(screen.getByText(/read-only share link/i)).toBeInTheDocument();
+
+    await user.keyboard('{Escape}');
+    expect(screen.queryByText(/read-only share link/i)).not.toBeInTheDocument();
+
+    await user.click(screen.getByRole('button', { name: /export/i }));
+    await user.click(screen.getByText(/scripture & chunks/i));
+    expect(screen.queryByRole('button', { name: /export markdown/i })).not.toBeInTheDocument();
+  });
+});