feat: add phase 1 runnable skeleton

apps/mobile/src/app/App.tsx

@@ -0,0 +1,26 @@
+import { type ReactNode, useState } from 'react';
+import { AppShell } from '../components/app-shell/AppShell.js';
+import { ActivityScreen } from '../screens/ActivityScreen/ActivityScreen.js';
+import { AskScreen } from '../screens/AskScreen/AskScreen.js';
+import { CronScreen } from '../screens/CronScreen/CronScreen.js';
+import { FilesScreen } from '../screens/FilesScreen/FilesScreen.js';
+import { SettingsScreen } from '../screens/SettingsScreen/SettingsScreen.js';
+import type { ScreenId } from './navigation.js';
+
+const screens: Record<ScreenId, ReactNode> = {
+  ask: <AskScreen />,
+  activity: <ActivityScreen />,
+  cron: <CronScreen />,
+  files: <FilesScreen />,
+  settings: <SettingsScreen />,
+};
+
+export function App() {
+  const [activeScreen, setActiveScreen] = useState<ScreenId>('ask');
+
+  return (
+    <AppShell activeScreen={activeScreen} onNavigate={setActiveScreen}>
+      {screens[activeScreen]}
+    </AppShell>
+  );
+}

apps/mobile/src/app/navigation.ts

@@ -0,0 +1,11 @@
+import { Activity, CalendarClock, Files, MessageCircle, Settings } from 'lucide-react';
+
+export const navItems = [
+  { id: 'ask', label: 'Ask', icon: MessageCircle },
+  { id: 'activity', label: 'Activity', icon: Activity },
+  { id: 'cron', label: 'Cron', icon: CalendarClock },
+  { id: 'files', label: 'Files', icon: Files },
+  { id: 'settings', label: 'Settings', icon: Settings },
+] as const;
+
+export type ScreenId = (typeof navItems)[number]['id'];