Applicatie afmaken en GUI-flow herstellen

Voegt boodschappenlijsten, productbeheer, realtime synchronisatie en browsercache-updates toe. Herstelt login- en sessiegedrag en maakt database-seeding herhaalbaar.\n\nCo-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

sockets/handlers.js

@@ -0,0 +1,12 @@
+const UserRepository = require("../repositories/UserRepository");
+
+module.exports = function registerSocketHandlers(io) {
+    io.on("connection", (socket) => {
+        const userId = socket.request.session && socket.request.session.userId;
+        const user = userId && UserRepository.findById(userId);
+        if (!user || !user.household_id) return socket.disconnect(true);
+
+        socket.join(`household:${user.household_id}`);
+        socket.on("list:join", (listId) => socket.join(`list:${listId}`));
+    });
+};