feat(android): a padlock icon instead of Delphi's default

Cyan on slate, the accent the desktop app already uses. Adaptive vectors for
Android 8+ - background covering the full 108 units since the launcher applies
its own mask, foreground kept inside the central 66 that no mask can crop -
plus a monochrome layer for Android 13 themed icons, where the keyhole has to
be a hole in the path rather than a shape in another colour.

PNGs for older launchers come from make-icons.ps1, same drawing, and carry
their own rounded square since nothing masks them.

They are copied over Delphi's in repack-apk.ps1, for the same reason as
libsk4d.so: the Android_LauncherIcon and Android_AdaptiveIcon properties ought
to be enough, and nothing deploys them here.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android-client/android-res/drawable/ic_launcher_background.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Fond de l'icone adaptative. Le systeme y applique son propre masque
+     (rond, carre arrondi, goutte selon le lanceur), donc il doit couvrir les
+     108 unites entieres : tout ce qui manque devient un bord blanc. -->
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="108"
+    android:viewportHeight="108">
+    <path
+        android:fillColor="#0F172A"
+        android:pathData="M0,0h108v108h-108z" />
+</vector>