feat(android): the system bars join the gradient

The app sat in a frame that did not belong to it: a grey status bar above, a WHITE navigation bar below, under a blue background. The reference bathes both in the same gradient, and that is what makes an app look like it occupies the screen rather than being placed on it.

Each bar takes one end of the gradient - top colour above, bottom colour below - so the continuity is exact. The FLAG_SECURE condition moved from the uses clause into the body of SecureScreen, since the same JNI imports now serve the bars, which must work in debug too.

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

mainApk.pas

@@ -240,6 +240,9 @@ begin
   // Qualifie : TForm a deja une methode PaintBackground, sans parametre, qui
   // masque celle de l'unite.
   PMA.Theme.PaintBackground(Fill);
+  // Les barres systeme prennent les deux extremites du degrade, pour que
+  // l'ecran soit d'un seul tenant.
+  TintSystemBars(COL_BG_TOP, COL_BG);
   SecureScreen;   // avant tout affichage de contenu
   FVault := TVault.Create;
   FIcons := TObjectDictionary<Integer, TBitmap>.Create([doOwnsValues]);