feat: add Expo QR code generation and modal for mobile preview

Introduce Expo QR code functionality to allow users to preview their projects on mobile devices. Added a new QR code modal component, integrated it into the chat and preview components, and implemented Expo URL detection in the shell process. This enhances the mobile development workflow by providing a seamless way to test Expo projects directly on devices.

- Clean up and consolidate Preview icon buttons while removing redundant ones.

app/components/workbench/ExpoQrModal.tsx

@@ -0,0 +1,43 @@
+import React from 'react';
+import { Dialog, DialogTitle, DialogDescription, DialogRoot } from '~/components/ui/Dialog';
+import { useStore } from '@nanostores/react';
+import { expoUrlAtom } from '~/stores/qrCodeStore';
+import QRCode from 'react-qr-code';
+
+interface ExpoQrModalProps {
+  open: boolean;
+  onClose: () => void;
+}
+
+export const ExpoQrModal: React.FC<ExpoQrModalProps> = ({ open, onClose }) => {
+  const expoUrl = useStore(expoUrlAtom);
+
+  return (
+    <DialogRoot open={open} onOpenChange={(v) => !v && onClose()}>
+      <Dialog
+        className="text-center !flex-col !mx-auto !text-center !max-w-md"
+        showCloseButton={true}
+        onClose={onClose}
+      >
+        <div className="border !border-bolt-elements-borderColor flex flex-col gap-5 justify-center items-center p-6 bg-bolt-elements-background-depth-2 rounded-md">
+          <div className="i-bolt:expo-brand h-10 w-full"></div>
+          <DialogTitle className="text-white text-lg font-semibold leading-6">
+            Preview on your own mobile device
+          </DialogTitle>
+          <DialogDescription className="bg-bolt-elements-background-depth-3 max-w-sm rounded-md p-1 border border-bolt-elements-borderColor">
+            Scan this QR code with the Expo Go app on your mobile device to open your project.
+          </DialogDescription>
+          <div className="my-6 flex flex-col items-center">
+            {expoUrl ? (
+              <div className="bg-white p-1 flex flex-col rounded-md justify-center items-center ">
+                <QRCode value={expoUrl} size={180} />
+              </div>
+            ) : (
+              <div className="text-gray-500 text-center">No Expo URL detected.</div>
+            )}
+          </div>
+        </div>
+      </Dialog>
+    </DialogRoot>
+  );
+};