refactor: Add missing file header

app/src/main/res/drawable/splashscreen_legacy.xml

@@ -1,3 +1,20 @@
+<!--
+  ~ Infomaniak SwissTransfer - Android
+  ~ Copyright (C) 2024 Infomaniak Network SA
+  ~
+  ~ This program is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by
+  ~ the Free Software Foundation, either version 3 of the License, or
+  ~ (at your option) any later version.
+  ~
+  ~ This program is distributed in the hope that it will be useful,
+  ~ but WITHOUT ANY WARRANTY; without even the implied warranty of
+  ~ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  ~ GNU General Public License for more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License
+  ~ along with this program.  If not, see <http://www.gnu.org/licenses/>.
+  -->
 <layer-list xmlns:android="http://schemas.android.com/apk/res/android">
 
     <item android:drawable="@drawable/splashscreen_gradient_legacy" />