fix(ux): apply UX quick wins (#54)

Get started links to registration and says an admin approves accounts.
Back navigation restores the library scroll; search no longer fills history.
Steam and PSN unlink ask first. Any close marks news as seen.
Confetti plays only when the level rises on the page.
Count-ups respect reduced motion. Html lang follows the UI language.
Add a 404 page, translated role and dialog close label.

src/pages/LandingPage.test.jsx

@@ -36,6 +36,21 @@ describe('LandingPage', () => {
         expect(screen.getByText('2025')).toBeTruthy();
     });
 
+    it('links "get started" to the registration and shows the approval hint, but not when logged in', async () => {
+        answer({});
+        const {unmount} = renderPage();
+
+        expect(screen.getByRole('link', {name: /MAIN.GET_STARTED/}).getAttribute('href')).toBe('/register');
+        expect(screen.getByText('MAIN.APPROVAL_HINT')).toBeTruthy();
+        await vi.waitFor(() => expect(fetch).toHaveBeenCalled());
+        unmount();
+
+        session.active = true;
+        renderPage();
+        expect(screen.queryByText('MAIN.APPROVAL_HINT')).toBeNull();
+        await vi.waitFor(() => expect(fetch).toHaveBeenCalled());
+    });
+
     it('hides the three blocks while their lists are empty', async () => {
         answer({gamesPerPlatform: [], topGenres: [], finishedPerYear: []});
         renderPage();