fix(android): declare FMX's biometric activity, and stop LoadVault from deleting the cache

The prompt raised ActivityNotFoundException: FMX does not show BiometricPrompt from our NativeActivity, it launches its own BiometricFragmentActivity, which lives in fmx.dex.jar but has to be declared in the manifest. Given a translucent framework theme - it hosts the system dialog and draws nothing itself, and the generated resources contain no AppCompat.

Then the read failed and the cache vanished with no trace. LoadVault sorted 'key lost' from 'not authenticated' on the exception message and deleted the file when it guessed the former - so a wrong guess destroyed the cache and the only record of why. It now reports through LastStoreError and deletes nothing; the caller has the log and the context. OpenLocalNow shows the reason, after ShowUnlock rather than before, which was overwriting it.

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

mainApk.pas

@@ -727,8 +727,11 @@ begin
   end
   else
   begin
-    Status('Coffre local illisible - retelechargement necessaire');
+    // ShowUnlock AVANT le message : il repositionne le statut selon ce que
+    // l'appareil detient, et ecraserait donc l'explication.
     ShowUnlock;
+    Log('Coffre local illisible : ' + LastStoreError);
+    Status('Coffre local illisible - voir le journal');
   end;
 end;