fix(mobile): add missing assets and EAS workflow for automatic builds

- Add mobile/assets/ directory with all required Expo/EAS asset files:
  - icon.png (1024x1024 branded app icon)
  - adaptive-icon.png (1024x1024 transparent fg for Android)
  - splash.png (1284x2778 branded splash screen)
  - favicon.png (48x48 web favicon)
  - notification-icon.png (96x96 white-on-transparent for Android)
  - notification-sound.wav (0.1s silent WAV, 44100 Hz mono)
- Add mobile/.eas/workflows/create-builds.yml for automatic production
  builds triggered on every push to main (per Expo EAS Workflows docs)

The Xcode image pin (macos-sequoia-15.1-xcode-16.2) was already present
in eas.json from the prior fix resolving the XCode 15.4 vs >=16.1 error.

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

mobile/.eas/workflows/create-builds.yml

@@ -0,0 +1,21 @@
+name: Create builds
+
+on:
+  push:
+    branches:
+      - main
+
+jobs:
+  build_android:
+    name: Build Android app
+    type: build
+    params:
+      platform: android
+      profile: production
+
+  build_ios:
+    name: Build iOS app
+    type: build
+    params:
+      platform: ios
+      profile: production