add toast notification system with success, error, and info variants

src/App.tsx

@@ -7,6 +7,7 @@ import { BoardList } from "@/components/boards/BoardList";
 import { BoardView } from "@/components/board/BoardView";
 import { CommandPalette } from "@/components/command-palette/CommandPalette";
 import { SettingsDialog } from "@/components/settings/SettingsDialog";
+import { ToastContainer } from "@/components/toast/ToastContainer";
 import { useKeyboardShortcuts } from "@/hooks/useKeyboardShortcuts";
 
 export default function App() {
@@ -64,6 +65,7 @@ export default function App() {
       </AppShell>
       <CommandPalette onOpenSettings={handleOpenSettings} />
       <SettingsDialog open={settingsOpen} onOpenChange={setSettingsOpen} />
+      <ToastContainer />
     </>
   );
 }