feat(audit): undo button for merges, hide manual games

The audit log shows Undo on a merge row for 30 days, with a confirm
dialog and clear errors. The details page follows a merged key to the
kept game. Hide and Show now work for manual games too. de/en texts.

src/pages/GameDetail.test.jsx

@@ -64,7 +64,7 @@ describe('GameDetail', () => {
     });
 
     it('keeps the game shown when Core refuses', async () => {
-        answer({...game, source: 'STEAM', hidden: false}, {'PUT /api/library/games/220/hidden': json(409, {code: 'MANUAL_GAME'})});
+        answer({...game, source: 'STEAM', hidden: false}, {'PUT /api/library/games/220/hidden': json(500, {})});
         renderDetail();
 
         fireEvent.click(await screen.findByRole('button', {name: 'GAME_DETAIL.HIDE'}));
@@ -73,12 +73,19 @@ describe('GameDetail', () => {
         expect(screen.queryByText('GAME_DETAIL.HIDDEN_NOTE')).toBeNull();
     });
 
-    it('offers no hide for a game added by hand', async () => {
-        answer({...game, source: 'MANUAL', platform: 'PS5', hidden: false});
-        renderDetail();
+    it('hides a game added by hand and shows it again', async () => {
+        answer({...game, appid: -1942, source: 'MANUAL', platform: 'PS5', hidden: false},
+            {'PUT /api/library/games/-1942/hidden': echo});
+        renderDetail(-1942);
 
-        await screen.findByText('GAME_DETAIL.OPEN_IN_STEAM');
-        expect(screen.queryByRole('button', {name: 'GAME_DETAIL.HIDE'})).toBeNull();
+        fireEvent.click(await screen.findByRole('button', {name: 'GAME_DETAIL.HIDE'}));
+
+        expect(await screen.findByText('GAME_DETAIL.HIDDEN_NOTE')).toBeTruthy();
+        expect(screen.queryByText('GAME_DETAIL.OPEN_IN_STEAM')).toBeNull();
+
+        fireEvent.click(screen.getByRole('button', {name: 'GAME_DETAIL.UNHIDE'}));
+
+        await waitFor(() => expect(screen.queryByText('GAME_DETAIL.HIDDEN_NOTE')).toBeNull());
     });
 
     it('reports a broken achievement icon once and shows the empty tile', async () => {
@@ -419,4 +426,16 @@ describe('GameDetail session', () => {
         expect(toast.error).not.toHaveBeenCalled();
         expect(screen.queryByText('GAME_DETAIL.ERROR_LOAD')).toBeNull();
     });
+
+    it('replacesTheUrlOfAMergedKeyWithTheKeptGame', async () => {
+        fetchRoutes({
+            'GET /api/users/me': json(200, {settings: {}}),
+            'GET /api/library/games/-7': json(200, {...game, appid: 220, source: 'STEAM'}),
+            'GET /api/library/games/220': json(200, {...game, appid: 220, source: 'STEAM'}),
+        });
+        const {router} = renderDetail(-7);
+
+        await waitFor(() => expect(router.state.location.pathname).toBe('/library/220'));
+        expect(router.state.historyAction).toBe('REPLACE');
+    });
 });