feat(HAI-002): build header and toast components

packages/dashboard/app/components/Header.tsx

@@ -0,0 +1,17 @@
+interface HeaderProps {
+  onNewTask: () => void;
+}
+
+export function Header({ onNewTask }: HeaderProps) {
+  return (
+    <header className="header">
+      <div className="header-left">
+        <h1 className="logo">hai</h1>
+        <span className="logo-sub">board</span>
+      </div>
+      <button className="btn btn-primary" onClick={onNewTask}>
+        + New Task
+      </button>
+    </header>
+  );
+}

packages/dashboard/app/components/ToastContainer.tsx

@@ -0,0 +1,18 @@
+import type { Toast } from "../hooks/useToast";
+
+interface ToastContainerProps {
+  toasts: Toast[];
+  onRemove: (id: number) => void;
+}
+
+export function ToastContainer({ toasts }: ToastContainerProps) {
+  return (
+    <div className="toast-container" id="toasts">
+      {toasts.map((toast) => (
+        <div key={toast.id} className={`toast toast-${toast.type}`}>
+          {toast.message}
+        </div>
+      ))}
+    </div>
+  );
+}