feat(questions): list and restore removed games

Add a "Removed games" section on the questions page and an Undo
toast after removing a manual game (#39).

README.md

@@ -281,6 +281,9 @@ flowchart LR
   live count) lists one card per game with an open question (Start it? / Finished? / Dropped? / Rate it?). Core decides
   which question is open; `src/utils/questions.js` only loads the list and sends the answer. A yes to Finished? gets
   the Rate it? card back at once. `409` / `404` reload the list. `RatingStars` is shared with `BacklogCard`.
+  Below the cards, a closed "Removed games" section (`RemovedGamesSection`, `GET /api/library/removed-games`) has a
+  Restore button per game (`POST /api/library/games/{appid}/restore`). The toast after "Remove from library" on a
+  manual game has an Undo that restores it the same way.
 
 ```mermaid
 flowchart LR
@@ -312,6 +315,7 @@ flowchart LR
     Header["AppHeader badge"] --> Count["Core /api/library/questions/count"]
     Page["QuestionsPage"] --> List["Core /api/library/questions"]
     Page -->|"Yes / No / stars"| Answer["Core POST /api/library/questions/{appid}"]
+    Page -->|"Removed games, Restore"| Removed["Core /api/library/removed-games, POST /games/{appid}/restore"]
 ```
 - Owner and user lists (`src/components/people/`, `src/utils/people.js`) need a login and show listed users by name
   (a link to `/u/<name>`), everyone else as "+N private", the viewer as "You". The setting "show me in owner lists" is