feat(onboarding): remove dead ends for new users (#55)

Registration shows the address used and can start over.
Confirm page says an admin approves; no login link.
Welcome puts next steps first; Steam link returns to the dashboard.
Dashboard and library explain an empty or private library.
First sync shows queued, polls slower up to 10 min, then a calm text.
Login: simple checks, resend offer after 401, password toggles.
Only a real expired link counts as invalid; typed passwords stay.
Default language follows the browser; texts are platform-neutral.

src/hooks/useLibrarySync.test.jsx

@@ -24,7 +24,7 @@ describe('useLibrarySync', () => {
         await act(() => vi.advanceTimersByTimeAsync(0));
         expect(result.current.isRunning).toBe(true);
 
-        await act(() => vi.advanceTimersByTimeAsync(125_000));
+        await act(() => vi.advanceTimersByTimeAsync(605_000));
 
         expect(result.current.isRunning).toBe(false);
         expect(result.current.stale).toBe(true);
@@ -33,6 +33,70 @@ describe('useLibrarySync', () => {
         expect(fetch.mock.calls.length).toBe(calls);
     });
 
+    it('isNotQueuedWhenDisabled', async () => {
+        fetchRoutes({});
+        const {result} = renderHook(() => useLibrarySync({enabled: false, expectInitialSync: true, onComplete: () => {}}));
+        await act(() => vi.advanceTimersByTimeAsync(0));
+
+        expect(result.current.queued).toBe(false);
+    });
+
+    it('is queued while a first sync is expected and Core has no status row', async () => {
+        fetchRoutes({'GET /api/library/sync-status': status(null, null)});
+        const {result} = renderHook(() => useLibrarySync({enabled: true, expectInitialSync: true, onComplete: () => {}}));
+        await act(() => vi.advanceTimersByTimeAsync(0));
+
+        expect(result.current.queued).toBe(true);
+    });
+
+    it('is not queued without expectInitialSync, or once a row exists', async () => {
+        fetchRoutes({'GET /api/library/sync-status': status(null, null)});
+        const first = renderHook(() => useLibrarySync({enabled: true, onComplete: () => {}}));
+        await act(() => vi.advanceTimersByTimeAsync(0));
+        expect(first.result.current.queued).toBe(false);
+        cleanup();
+
+        fetchRoutes({'GET /api/library/sync-status': status('RUNNING', null)});
+        const second = renderHook(() => useLibrarySync({enabled: true, expectInitialSync: true, onComplete: () => {}}));
+        await act(() => vi.advanceTimersByTimeAsync(0));
+        expect(second.result.current.queued).toBe(false);
+    });
+
+    it('polls every 3 s for 15 s while queued, then every 15 s, and stops after 10 minutes', async () => {
+        const fetch = fetchRoutes({'GET /api/library/sync-status': status(null, null)});
+        renderHook(() => useLibrarySync({enabled: true, expectInitialSync: true, onComplete: () => {}}));
+        await act(() => vi.advanceTimersByTimeAsync(0));
+        expect(fetch.mock.calls.length).toBe(1);
+
+        await act(() => vi.advanceTimersByTimeAsync(15_000));
+        expect(fetch.mock.calls.length).toBe(6);
+
+        await act(() => vi.advanceTimersByTimeAsync(60_000));
+        expect(fetch.mock.calls.length).toBe(10);
+
+        await act(() => vi.advanceTimersByTimeAsync(600_000));
+        const calls = fetch.mock.calls.length;
+        await act(() => vi.advanceTimersByTimeAsync(60_000));
+        expect(fetch.mock.calls.length).toBe(calls);
+    });
+
+    it('still sees a first sync that starts after one minute', async () => {
+        let answer = status(null, null);
+        fetchRoutes({'GET /api/library/sync-status': () => answer});
+        const onComplete = vi.fn();
+        const {result} = renderHook(() => useLibrarySync({enabled: true, expectInitialSync: true, onComplete}));
+        await act(() => vi.advanceTimersByTimeAsync(60_000));
+        expect(result.current.isRunning).toBe(false);
+
+        answer = status('RUNNING', null);
+        await act(() => vi.advanceTimersByTimeAsync(15_000));
+        expect(result.current.isRunning).toBe(true);
+
+        answer = status('OK', '2026-10-21T08:00:00Z');
+        await act(() => vi.advanceTimersByTimeAsync(15_000));
+        expect(onComplete).toHaveBeenCalledTimes(1);
+    });
+
     it('after watch() reports the end of a sync once, also when it never saw it running', async () => {
         let answer = status('OK', '2026-09-30T08:00:00Z');
         fetchRoutes({'GET /api/library/sync-status': () => answer});