Add root ErrorBoundary to both apps, simplify withDb

Both apps now have proper ErrorBoundary exports in root.tsx:
- 404: "Page not found"
- 503: "Service temporarily unavailable"
- Other: shows error message

Simplified withDb re-throw check: anything with a "status" property
is treated as a React Router response (covers Response and
ErrorResponseImpl). DB errors throw a plain Response(503) that
the error boundary renders nicely.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/planner/app/root.tsx

@@ -1,5 +1,6 @@
-import { Links, Meta, Outlet, Scripts, ScrollRestoration } from "react-router";
+import { Links, Meta, Outlet, Scripts, ScrollRestoration, isRouteErrorResponse } from "react-router";
 import type { LinksFunction } from "react-router";
+import type { Route } from "./+types/root";
 import stylesheet from "@trails-cool/ui/styles.css?url";
 
 export const links: LinksFunction = () => [{ rel: "stylesheet", href: stylesheet }];
@@ -25,3 +26,31 @@ export function Layout({ children }: { children: React.ReactNode }) {
 export default function App() {
   return <Outlet />;
 }
+
+export function ErrorBoundary({ error }: Route.ErrorBoundaryProps) {
+  if (isRouteErrorResponse(error)) {
+    return (
+      <div className="flex h-full items-center justify-center">
+        <div className="text-center">
+          <h1 className="text-4xl font-bold text-gray-900">{error.status}</h1>
+          <p className="mt-2 text-gray-600">
+            {error.status === 404 && "Page not found"}
+            {error.status === 503 && "Service temporarily unavailable"}
+            {error.status !== 404 && error.status !== 503 && (error.statusText || "Something went wrong")}
+          </p>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="flex h-full items-center justify-center">
+      <div className="text-center">
+        <h1 className="text-4xl font-bold text-gray-900">Error</h1>
+        <p className="mt-2 text-gray-600">
+          {error instanceof Error ? error.message : "An unexpected error occurred"}
+        </p>
+      </div>
+    </div>
+  );
+}