fix: TypeScript-Fehler behoben (stockfish types, null-Typ)

server/src/types/stockfish.d.ts

@@ -0,0 +1,9 @@
+declare module "stockfish" {
+    interface StockfishInstance {
+        postMessage(cmd: string): void;
+        onmessage: ((line: string | { data: string }) => void) | null;
+        terminate?: () => void;
+    }
+    function Stockfish(): StockfishInstance;
+    export default Stockfish;
+}