fix(mobile): upgrade Expo SDK from 51 to 54 and fix EAS project ID

- Update mobile/app.json: replace YOUR_EAS_PROJECT_ID placeholder with
  the real EAS project ID (8455f39d-ef0d-4850-98e4-f79e388642c1)
- Update mobile/package.json: upgrade all dependencies to Expo SDK 54
  compatible versions (react 19.1.0, react-native 0.81.5, expo ~54.0.0,
  all expo-* packages, react-navigation v6 → v7, @types/react ~19.1.10)
- Update mobile/README.md: remove outdated eas init step, document that
  the EAS project ID is already configured and explain when to update it

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

mobile/README.md

@@ -43,9 +43,6 @@ npm install -g eas-cli
 # Log in to Expo
 eas login
 
-# Configure your project (one-time) – updates app.json with the EAS project ID
-eas init
-
 # Build for iOS
 eas build --platform ios
 
@@ -56,7 +53,7 @@ eas build --platform android
 eas build --platform all
 ```
 
-> **After running `eas init`:** update the `extra.eas.projectId` field in `app.json` with the value printed by the command.
+> **Note:** The EAS project ID is already configured in `app.json` (`extra.eas.projectId`). You only need to run `eas init` if you are setting up a fork or a brand-new EAS project — in that case, replace the `extra.eas.projectId` value in `app.json` with the ID printed by `eas init`.
 
 ### iOS-specific