fix(frontend): projet Android complet (embedding v2) pour build web Docker

- Régénération android/ (MainActivity, Gradle, manifestes, icônes)
- gradle-wrapper.jar versionné (wrapper requis hors machine locale)
- Ignore local.properties à la racine du dépôt
- pubspec.lock / .metadata alignés Flutter 3.19 (résolution pub get CI)

Made-with: Cursor

frontend/android/app/src/main/res/drawable-v21/launch_background.xml

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="?android:colorBackground" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>