feat(tictactoe): integrate leaderboard UI, provider API hook, and new styles

- Add *_BKP* ignore rule to .gitignore
- Insert Leaderboard component into TicTacToe screen
- Add getLeaderboardTop() API method to NakamaProvider and expose via context
- Add full leaderboard polling logic (interval-based) in new Leaderboard.tsx
- Style leaderboard in styles.css (rows, rank, name, score, empty state, card UI)
- Modernize TicTacToe UI styles (board, squares, buttons, layout)
- Replace matchmaking view with leaderboard integration
- Import ApiLeaderboardRecordList and ApiMatch types cleanly

src/tictactoe/TicTacToe.tsx

@@ -1,7 +1,8 @@
 import { useState, useEffect } from "react";
 import { useNakama } from "./providers/NakamaProvider";
-import { Match } from "@heroiclabs/nakama-js";
 import Board from "./Board";
+import Leaderboard from "./Leaderboard";
+// import { Match } from "@heroiclabs/nakama-js";
 // import MatchList from "./MatchList";
 
 export default function TicTacToe() {
@@ -143,6 +144,7 @@ export default function TicTacToe() {
 
           {/*/!* List open matches *!/*/}
           {/*<MatchList matches={openMatches} />*/}
+          <Leaderboard/>
         </>
       )}