feat: 1-to-1 message render + web data-lake backend

frontend/src/lib/stores/toasts.svelte.ts

@@ -0,0 +1,47 @@
+type ToastType = "info" | "error" | "success";
+
+interface Toast {
+  id: number;
+  message: string;
+  type: ToastType;
+}
+
+const DEFAULT_TIMEOUT = 4000;
+
+function createToasts() {
+  let items = $state<Toast[]>([]);
+  let nextId = 0;
+
+  function dismiss(id: number) {
+    items = items.filter((toast) => toast.id !== id);
+  }
+
+  function show(
+    message: string,
+    type: ToastType = "info",
+    timeout = DEFAULT_TIMEOUT
+  ) {
+    const id = nextId++;
+    items = [...items, { id, type, message }];
+    if (timeout > 0) {
+      setTimeout(() => dismiss(id), timeout);
+    }
+    return id;
+  }
+
+  return {
+    get items() {
+      return items;
+    },
+    show,
+    error(message: string) {
+      return show(message, "error");
+    },
+    success(message: string) {
+      return show(message, "success");
+    },
+    dismiss,
+  };
+}
+
+export const toasts = createToasts();