Android: fix black gap above keyboard (SafeArea/SystemBars config)

The safe-area plugin logged: set SystemBars.insetsHandling to "disable". Under
Android edge-to-edge (targetSdk 36) this + offsetForKeyboardInsetBug were causing
a black strip between the input and the soft keyboard on the login view. Set
SystemBars.insetsHandling="disable" and SafeArea.offsetForKeyboardInsetBug=true.
Native config — takes effect on the next Android build; verify on device.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

mobile/capacitor.config.json

@@ -14,7 +14,10 @@
     "SafeArea": {
       "detectViewportFitCoverChanges": true,
       "initialViewportFitCover": true,
-      "offsetForKeyboardInsetBug": false
+      "offsetForKeyboardInsetBug": true
+    },
+    "SystemBars": {
+      "insetsHandling": "disable"
     },
     "Keyboard": {
       "resize": "none"