fix(mobile): add root index.tsx redirect to prevent stale Hello World screen

Without a root app/index.tsx in the repo, a stale default Expo Router
scaffold file (showing "Hello World") could be picked up from a previous
build or CLI scaffolding and displayed instead of the real app.

The new index.tsx immediately redirects to /(auth)/, and the existing
AuthGuard in _layout.tsx forwards authenticated users to /(tabs)/.

Also registers the index screen in the root Stack and updates
docs/MobileApp.md with an expanded project structure and a new
troubleshooting entry.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

docs/MobileApp.md

@@ -279,7 +279,19 @@ If you wish to use **direct FCM/APNs** without Expo's relay, replace the `send_e
 
 ```
 mobile/
-├── App.tsx                      # Root component
+├── App.tsx                      # Root component (legacy, not used at runtime)
+├── app/                         # Expo Router file-based routes
+│   ├── _layout.tsx              # Root layout (AuthGuard + providers)
+│   ├── index.tsx                # Root redirect → /(auth)/
+│   ├── (auth)/                  # Unauthenticated route group
+│   │   ├── _layout.tsx          # Stack navigator (headerless)
+│   │   ├── index.tsx            # Welcome screen
+│   │   └── login.tsx            # Login screen
+│   └── (tabs)/                  # Authenticated route group
+│       ├── _layout.tsx          # Tab navigator
+│       ├── index.tsx            # Upload screen (default tab)
+│       ├── files.tsx            # Files screen
+│       └── profile.tsx          # Profile screen
 ├── app.json                     # Expo/EAS configuration
 ├── eas.json                     # EAS Build profiles
 ├── package.json
@@ -301,6 +313,25 @@ mobile/
 
 ## Troubleshooting
 
+### App shows "Hello World" / default Expo page after update
+
+If the iOS or Android app shows a generic "Hello World – This is the first page of your app" screen instead of the DocuElevate UI, it means a stale default `index.tsx` file (generated by Expo CLI scaffolding) is being picked up in the `mobile/app/` directory.
+
+**To fix:**
+
+1. Delete any leftover default `mobile/app/index.tsx` that is **not** the repository version (the repo version contains a `<Redirect>` to `/(auth)/`).
+2. Clear the Metro bundler cache and rebuild:
+   ```bash
+   cd mobile
+   npx expo start --clear
+   ```
+3. For production builds, run a clean EAS build:
+   ```bash
+   eas build --platform ios --clear-cache
+   ```
+
+The repository includes a root `app/index.tsx` that immediately redirects to the authentication flow, so this issue should not recur once the correct file is present.
+
 ### "Session expired Local session" during iOS build
 
 EAS stores an Apple ID session locally (in `~/.expo/`) to manage code-signing certificates and provisioning profiles.  This session expires after a few weeks.

mobile/app/_layout.tsx

@@ -118,6 +118,7 @@ function AuthGuard() {
 
   return (
     <Stack screenOptions={{ headerShown: false }}>
+      <Stack.Screen name="index" />
       <Stack.Screen name="(auth)" />
       <Stack.Screen name="(tabs)" />
     </Stack>

mobile/app/index.tsx

@@ -0,0 +1,17 @@
+/**
+ * Root index route – redirects to the auth flow on launch.
+ *
+ * expo-router renders this when the "/" route is matched (i.e. on cold start).
+ * Without this file, a stale default scaffold page ("Hello World") can appear
+ * if one was left behind by a previous build or Expo CLI scaffolding.
+ *
+ * The redirect targets the (auth) group; the AuthGuard in _layout.tsx will
+ * immediately forward authenticated users to (tabs).
+ */
+
+import { Redirect } from "expo-router";
+import React from "react";
+
+export default function RootIndex() {
+  return <Redirect href="/(auth)/" />;
+}