feat(app): add setup hint and paseo.sh link on mobile welcome screen

New app store users land on the welcome screen with no context. Show a
brief explanation that the desktop app or server is needed, plus a link
to paseo.sh — only on mobile (iOS/Android), hidden on web/desktop.

packages/app/src/components/welcome-screen.tsx

@@ -2,7 +2,7 @@ import { useCallback, useEffect, useState, useSyncExternalStore } from "react";
 import { Pressable, Text, View, Platform, ScrollView } from "react-native";
 import { useRouter } from "expo-router";
 import { StyleSheet, useUnistyles } from "react-native-unistyles";
-import { QrCode, Link2, ClipboardPaste } from "lucide-react-native";
+import { QrCode, Link2, ClipboardPaste, ExternalLink } from "lucide-react-native";
 import { useSafeAreaInsets } from "react-native-safe-area-context";
 import type { HostProfile } from "@/types/host-connection";
 import {
@@ -20,6 +20,7 @@ import { resolveAppVersion } from "@/utils/app-version";
 import { formatVersionWithPrefix } from "@/desktop/updates/desktop-updates";
 import { buildHostRootRoute } from "@/utils/host-routes";
 import { PaseoLogo } from "@/components/icons/paseo-logo";
+import { openExternalUrl } from "@/utils/open-external-url";
 
 type WelcomeAction = {
   key: "scan-qr" | "direct-connection" | "paste-pairing-link";
@@ -118,6 +119,25 @@ const styles = StyleSheet.create((theme) => ({
     color: theme.colors.destructive,
     fontSize: theme.fontSize.sm,
   },
+  setupHint: {
+    color: theme.colors.foregroundMuted,
+    fontSize: theme.fontSize.sm,
+    textAlign: "center",
+    marginBottom: theme.spacing[6],
+    lineHeight: theme.fontSize.sm * 1.5,
+  },
+  setupLink: {
+    flexDirection: "row",
+    alignItems: "center",
+    justifyContent: "center",
+    gap: 6,
+    marginBottom: theme.spacing[6],
+  },
+  setupLinkText: {
+    color: theme.colors.accent,
+    fontSize: theme.fontSize.sm,
+    fontWeight: theme.fontWeight.medium,
+  },
   versionLabel: {
     color: theme.colors.foregroundMuted,
     fontSize: theme.fontSize.xs,
@@ -326,6 +346,21 @@ export function WelcomeScreen({ onHostAdded }: WelcomeScreenProps) {
           {showHostList ? "Connecting to your hosts…" : "Connect to your host to start"}
         </Text>
 
+        {!showHostList && Platform.OS !== "web" && (
+          <>
+            <Text style={styles.setupHint}>
+              You need the Paseo desktop app or server running on your computer first.
+            </Text>
+            <Pressable
+              style={styles.setupLink}
+              onPress={() => openExternalUrl("https://paseo.sh")}
+            >
+              <Text style={styles.setupLinkText}>Get started at paseo.sh</Text>
+              <ExternalLink size={14} color={theme.colors.accent} />
+            </Pressable>
+          </>
+        )}
+
         <View style={styles.actions}>
           {actions.map((action) => {
             const Icon = action.icon;