feat: podpora high-availability a multi-replica nasazení

- Socket.io Redis adapter pro sdílený stav přes repliky
- graceful shutdown serveru
- WATCH/MULTI v updateData pro race-condition-safe aktualizace
- lease mechanismus pro push reminder (zabrání duplicitnímu odesílání)
- k8s/ manifesty pro testovací kind cluster
- Dockerfile: opraven EXPOSE port na 3001
- .gitignore: ignorovány Claude pracovní soubory

server/src/websocket.ts

@@ -1,12 +1,15 @@
 import { DefaultEventsMap, Server } from "socket.io";
+import { createAdapter } from "@socket.io/redis-adapter";
+import { createClient } from "redis";
 
 let io: Server<DefaultEventsMap, DefaultEventsMap, DefaultEventsMap, any>;
+let pubClient: ReturnType<typeof createClient>;
+let subClient: ReturnType<typeof createClient>;
 
 export const initWebsocket = (server: any) => {
     io = new Server(server, {
-        cors: {
-            origin: "*",
-        },
+        cors: { origin: "*" },
+        transports: ["websocket"],
     });
     io.on("connection", (socket) => {
         console.log(`New client connected: ${socket.id}`);
@@ -26,7 +29,24 @@ export const initWebsocket = (server: any) => {
         });
     });
     return io;
-}
+};
+
+/** Připojí Redis adapter pro cross-pod broadcasting. Volat až po inicializaci Redis klienta. */
+export const initRedisAdapter = async () => {
+    const HOST = process.env.REDIS_HOST ?? 'localhost';
+    const PORT = process.env.REDIS_PORT ?? 6379;
+    const url = `redis://${HOST}:${PORT}`;
+    pubClient = createClient({ url }) as ReturnType<typeof createClient>;
+    subClient = pubClient.duplicate();
+    await Promise.all([pubClient.connect(), subClient.connect()]);
+    io.adapter(createAdapter(pubClient as any, subClient as any));
+    console.log('Socket.io: Redis adapter connected');
+};
+
+/** Zavře pub/sub Redis klienty adaptéru při graceful shutdown. */
+export const shutdownWebsocketClients = async () => {
+    await Promise.allSettled([pubClient?.quit(), subClient?.quit()]);
+};
 
 export const getWebsocket = () => io;
 
@@ -34,4 +54,4 @@ export const getWebsocket = () => io;
 export const emitToUser = (login: string, event: string, data: unknown) => {
     if (!io) return;
     io.to(`user:${login}`).emit(event, data);
-}
+};