fix: handle stockfish process error, try /usr/games/stockfish path

server/src/controllers/stockfish.controller.ts

@@ -30,10 +30,21 @@ export class StockfishEngine {
 
     private async init() {
         try {
-            this.process = spawn("stockfish", [], {
+            // Debian installs stockfish to /usr/games/stockfish
+            const sfBin = ["/usr/games/stockfish", "/usr/bin/stockfish", "stockfish"]
+                .find(p => { try { require("fs").accessSync(p); return true; } catch { return false; } })
+                ?? "stockfish";
+
+            this.process = spawn(sfBin, [], {
                 stdio: ["pipe", "pipe", "pipe"],
             });
 
+            this.process.on("error", (err) => {
+                console.error("Stockfish process error:", err.message);
+                this.process = null;
+                this.ready = false;
+            });
+
             await new Promise<void>((resolve) => {
                 let readyOk = false;