feat(21-01): add ErrorBoundary, Sonner toast provider, and 404 navigation

- Create ErrorBoundary class component with recovery UI (reload button)
- Create Sonner Toaster wrapper (bottom-right, richColors)
- Wire ErrorBoundary around Outlet in root route to catch render errors
- Add Toaster as sibling to AppLayout in root route
- Update notFoundComponent with Back to Dashboard link button

package-lock.json

@@ -5984,6 +5984,16 @@
         "url": "https://github.com/steveukx/git-js?sponsor=1"
       }
     },
+    "node_modules/sonner": {
+      "version": "2.0.7",
+      "resolved": "https://registry.npmjs.org/sonner/-/sonner-2.0.7.tgz",
+      "integrity": "sha512-W6ZN4p58k8aDKA4XPcx2hpIQXBRAgyiWVkYhT7CvK6D3iAu7xjvVyhQHg2/iaKJZ1XVJ4r7XuwGL+WGEK37i9w==",
+      "license": "MIT",
+      "peerDependencies": {
+        "react": "^18.0.0 || ^19.0.0 || ^19.0.0-rc",
+        "react-dom": "^18.0.0 || ^19.0.0 || ^19.0.0-rc"
+      }
+    },
     "node_modules/source-map": {
       "version": "0.6.1",
       "resolved": "https://registry.npmjs.org/source-map/-/source-map-0.6.1.tgz",
@@ -6725,6 +6735,7 @@
         "lucide-react": "^0.563.0",
         "react": "^19.0.0",
         "react-dom": "^19.0.0",
+        "sonner": "^2.0.7",
         "tailwind-merge": "^3.4.0"
       },
       "devDependencies": {

packages/web/package.json

@@ -22,6 +22,7 @@
     "lucide-react": "^0.563.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
+    "sonner": "^2.0.7",
     "tailwind-merge": "^3.4.0"
   },
   "devDependencies": {

packages/web/src/components/ErrorBoundary.tsx

@@ -0,0 +1,54 @@
+import { Component } from "react";
+import type { ErrorInfo, ReactNode } from "react";
+import { AlertCircle } from "lucide-react";
+import { Button } from "@/components/ui/button";
+
+interface ErrorBoundaryProps {
+  children: ReactNode;
+}
+
+interface ErrorBoundaryState {
+  hasError: boolean;
+  error: Error | null;
+}
+
+export class ErrorBoundary extends Component<
+  ErrorBoundaryProps,
+  ErrorBoundaryState
+> {
+  constructor(props: ErrorBoundaryProps) {
+    super(props);
+    this.state = { hasError: false, error: null };
+  }
+
+  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
+    return { hasError: true, error };
+  }
+
+  componentDidCatch(error: Error, errorInfo: ErrorInfo): void {
+    console.error("ErrorBoundary caught an error:", error, errorInfo);
+  }
+
+  handleReload = () => {
+    window.location.reload();
+  };
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div className="flex flex-col items-center justify-center gap-4 py-12">
+          <AlertCircle className="h-8 w-8 text-destructive" />
+          <h2 className="text-lg font-semibold">Something went wrong</h2>
+          <p className="max-w-md text-center text-sm text-muted-foreground">
+            {this.state.error?.message ?? "An unexpected error occurred."}
+          </p>
+          <Button variant="outline" size="sm" onClick={this.handleReload}>
+            Reload
+          </Button>
+        </div>
+      );
+    }
+
+    return this.props.children;
+  }
+}

packages/web/src/components/ui/sonner.tsx

@@ -0,0 +1,13 @@
+import { Toaster as SonnerToaster } from "sonner";
+
+export function Toaster() {
+  return (
+    <SonnerToaster
+      position="bottom-right"
+      richColors
+      toastOptions={{
+        className: "font-sans",
+      }}
+    />
+  );
+}

packages/web/src/routes/__root.tsx

@@ -1,16 +1,27 @@
-import { createRootRoute, Outlet } from '@tanstack/react-router'
+import { createRootRoute, Link, Outlet } from '@tanstack/react-router'
 import { AppLayout } from '../layouts/AppLayout'
+import { ErrorBoundary } from '../components/ErrorBoundary'
+import { Toaster } from '../components/ui/sonner'
+import { Button } from '../components/ui/button'
 
 export const Route = createRootRoute({
   component: () => (
-    <AppLayout>
-      <Outlet />
-    </AppLayout>
+    <>
+      <AppLayout>
+        <ErrorBoundary>
+          <Outlet />
+        </ErrorBoundary>
+      </AppLayout>
+      <Toaster />
+    </>
   ),
   notFoundComponent: () => (
-    <div className="p-8 text-center">
+    <div className="flex flex-col items-center justify-center gap-4 py-12">
       <h1 className="text-2xl font-bold">Page not found</h1>
-      <p className="text-muted-foreground mt-2">The page you are looking for does not exist.</p>
+      <p className="text-muted-foreground">The page you are looking for does not exist.</p>
+      <Button variant="outline" asChild>
+        <Link to="/initiatives">Back to Dashboard</Link>
+      </Button>
     </div>
   ),
 })