fix(mobile): lock in device-independent keyboard (VisualViewport residual), remove debug

Debug confirmed resize:native shrinks the WebView by the keyboard height, so the composer only needs the
residual lift = clientHeight - visualViewport.height (46px on the test device — the prediction-bar sliver).
Tracked live via VisualViewport so it follows the keyboard. Zero per-device constants. Removed debug bar;
reverted Keyboard config to resize:native (which the logic relies on).
Build marker -> 2026-07-18-batch105.

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

mobile/capacitor.config.json

@@ -17,7 +17,7 @@
       "offsetForKeyboardInsetBug": false
     },
     "Keyboard": {
-      "resize": "none"
+      "resize": "native"
     },
     "SplashScreen": {
       "launchShowDuration": 900,